Re: [f2fs-dev] [PATCH 07/20] f2fs: support subpage blocks in data write path and writeback

[Daeho Jeong]

On Tue, Nov 10, 2026 at 3:19 AM Chao Yu <chao@xxxxxxxxxx> wrote:
>
> On 11/8/26 07:14, Daeho Jeong wrote:
> > On Thu, Nov 5, 2026 at 6:52 PM Chao Yu <chao@xxxxxxxxxx> wrote:
> >>
> >> On 11/3/26 03:39, Daeho Jeong wrote:
> >>> From: Daeho Jeong <daehojeong@xxxxxxxxxx>
> >>>
> >>> With blocks smaller than PAGE_SIZE, a folio holds several blocks, so
> >>> write_begin, write_end and writeback have to handle individual blocks
> >>> instead of the whole folio.
> >>>
> >>> - Read, zero and reserve the blocks touched by a write per block in
> >>>    write_begin, and mark only the written blocks dirty in write_end.
> >>> - Write back only the dirty blocks of a multi-block folio and complete
> >>>    write I/O per block. In subpage mode every inode is written back by
> >>>    f2fs_write_cache_folios(), which now handles dentry and quota folios
> >>>    and checkpoint errors as f2fs_write_single_data_page() does. Both use
> >>>    the new f2fs_cp_controlled_inode() and f2fs_wb_folio_action() helpers
> >>>    for these rules.
> >>>    It also resets the error for each folio, so that the remaining folios
> >>>    are still written back after an error, as writeback_iter() expects
> >>>    for integrity writeback, instead of redirtying them.
> >>>    f2fs_write_folio_dirty_range() cleans up each block where it is
> >>>    written or skipped, and advances last_disk_size only up to the last
> >>>    block it submitted. On an error, it clears the dirty state of the
> >>>    blocks before the failed one, so that only the failed block and the
> >>>    ones after it are written again.
> >>> - Count inode dirty blocks per folio: add all blocks of a folio when
> >>>    it is dirtied and remove them when it is cleaned, instead of counting
> >>>    the dirty bits of the folio state. A multi-block folio can be dirtied
> >>>    without a folio state, e.g. after a read of the whole folio or
> >>>    through folio_mark_dirty(), and a state attached later starts with
> >>>    dirty bits that were never counted, so the bit count cannot stay
> >>>    balanced. A partially dirty folio is counted as fully dirty.
> >>
> >> Sorry, still I don't understand why we can not track dirty block count in folio,
> >> the count should be consistent w/ dirty bitmap in ffs (e.g. if there is x bits in
> >> bitmap is 1, the count should be x).
> >>
> >> IIUC, if large folio can track dirty page count, 16k-page should can track 4k
> >> dirty block as well? or is there any difference in subpage block feature, can you
> >> please explain more about this?
> >
> > Hi Chao,
>
> Hi Daeho,
>
> Thanks for the detailed explanation.
>
> >
> > Counting dirty bits needs the folio state on every dirty multi-block
> > folio, but a folio can be dirtied through ->dirty_folio(), which cannot
> > allocate it: ->dirty_folio() must not block and can be called under
> > the page table lock without the folio lock, and it has no range, so the
> > whole folio becomes dirty. E.g. a folio read by a single bio has no
> > folio state, and it can then be dirtied by GUP or mmap. When the folio
> > state is attached later, its dirty bits are set from PG_dirty, and
> > these bits were never counted, so clearing them unbalances the counter.
>
> I think for such case that GUP or mmap set folio dirty, since the entire folio
> is dirty:
> 1. w/o ffs, we can just increase reference w/ blks_per_folio.
> 2. w/ ffs, we can update fss dirty bitmap, and increase reference w/ blks count
> that they are not dirty previously.
>
> >
> > Large folios worked because the folio state was attached up front, but
> > in subpage mode every order-0 folio is a multi-block folio, and we
> > cannot attach it in every path that creates or dirties a folio.
> > Counting per folio adds and removes the same number when the folio is
> > dirtied and cleaned, so it always stays balanced. A partially dirty
> > folio is counted as fully dirty, but the counters are only compared
> > with thresholds such as min_fsync_blocks, and order-0 folios were
> > counted per page before, so this is enough.
>
> However there is a side-effect, F2FS_DIRTY_DENTS will not match the real
> dirty dentry block count? result in has_not_enough_free_secs() return
> true earlier and trigger unnecessary fggc?
>

Hi Chao,

In v1, I tried a simpler way to make it work first. Now, we could take the way
you say. If a folio is counted as blks_per_folio without a folio state, and
the count is adjusted to its dirty bits when a folio state is attached, the
counter stays balanced.

In v2, I'll count the dirty bits again:
- ->dirty_folio() marks the uptodate blocks within EOF dirty and counts the
  newly dirty ones for a folio with a folio state, and counts
  blks_per_folio for a folio without it.
- The updates made by f2fs itself mark and count only the blocks they
  modify, and do not go through ->dirty_folio().
- Attaching a folio state to a dirty folio converts its count to the dirty
  bits.

> >
> >>
> >>> - Compressed and atomic files are not supported yet in subpage mode:
> >>>    write_begin returns -EOPNOTSUPP for them. Inline data is converted
> >>>    first.
> >>>
> >>> Some of these changes also apply to large folios when the block size
> >>> equals PAGE_SIZE.
> >>>
> >>> Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
> >>> ---
> >>>   fs/f2fs/checkpoint.c |  39 +---
> >>>   fs/f2fs/data.c       | 486 ++++++++++++++++++++++---------------------
> >>>   fs/f2fs/dir.c        |   2 +-
> >>>   fs/f2fs/f2fs.h       |   1 -
> >>>   fs/f2fs/file.c       |  11 +-
> >>>   fs/f2fs/gc.c         |  11 +-
> >>>   fs/f2fs/inline.c     |   7 +-
> >>>   fs/f2fs/node.c       |   2 +-
> >>>   8 files changed, 275 insertions(+), 284 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>> index 1060ee651756..a9a2b9d93231 100644
> >>> --- a/fs/f2fs/checkpoint.c
> >>> +++ b/fs/f2fs/checkpoint.c
> >>> @@ -1324,46 +1324,21 @@ static void __remove_dirty_inode(struct inode *inode, enum inode_type type)
> >>>       stat_dec_dirty_inode(F2FS_I_SB(inode), type);
> >>>   }
> >>>
> >>> -/*
> >>> - * Account @nr dirty blocks (negative when dirtiness is cleared) for @inode.
> >>> - */
> >>> -void f2fs_account_dirty_blocks(struct inode *inode, int nr)
> >>> +void f2fs_update_dirty_folio(struct inode *inode, struct folio *folio)
> >>>   {
> >>>       struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >>>       enum inode_type type = S_ISDIR(inode->i_mode) ? DIR_INODE : FILE_INODE;
> >>> +     unsigned int nr_blocks = f2fs_blocks_per_folio(sbi, folio);
> >>>
> >>> -     if (!nr)
> >>> -             return;
> >>> -
> >>> -     spin_lock(&sbi->inode_lock[type]);
> >>> -     if (nr > 0) {
> >>> -             if (type != FILE_INODE || test_opt(sbi, DATA_FLUSH))
> >>> -                     __add_dirty_inode(inode, type);
> >>> -             inode_add_dirty_blocks(inode, nr);
> >>> -     } else {
> >>> -             inode_sub_dirty_blocks(inode, -nr);
> >>> -             __remove_dirty_inode(inode, type);
> >>> -     }
> >>> -     spin_unlock(&sbi->inode_lock[type]);
> >>> -}
> >>> -
> >>> -void f2fs_update_dirty_folio(struct inode *inode, struct folio *folio)
> >>> -{
> >>>       if (!S_ISDIR(inode->i_mode) && !S_ISREG(inode->i_mode) &&
> >>>                       !S_ISLNK(inode->i_mode))
> >>>               return;
> >>>
> >>> -     /*
> >>> -      * Large folios have a subpage dirty bitmap, so defer their dirty accounting
> >>> -      * to the f2fs_ffs_*subrange_dirty*() helpers.  This avoids nesting
> >>> -      * ffs->state_lock with the inode dirty list lock.
> >>> -      */
> >>> -     if (f2fs_folio_has_ffs(folio)) {
> >>> -             folio_set_f2fs_reference(folio);
> >>> -             return;
> >>> -     }
> >>> -
> >>> -     f2fs_account_dirty_blocks(inode, 1);
> >>> +     spin_lock(&sbi->inode_lock[type]);
> >>> +     if (type != FILE_INODE || test_opt(sbi, DATA_FLUSH))
> >>> +             __add_dirty_inode(inode, type);
> >>> +     inode_add_dirty_blocks(inode, nr_blocks);
> >>> +     spin_unlock(&sbi->inode_lock[type]);
> >>>
> >>>       folio_set_f2fs_reference(folio);
> >>>   }
> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >>> index 07b7aeb94350..41246f83b31d 100644
> >>> --- a/fs/f2fs/data.c
> >>> +++ b/fs/f2fs/data.c
> >>> @@ -420,8 +420,7 @@ static void f2fs_write_end_bio(struct bio *bio)
> >>>
> >>>       bio_for_each_folio_all(fi, bio) {
> >>>               struct folio *folio = fi.folio;
> >>> -             unsigned int nr_pages = fi.length >> PAGE_SHIFT;
> >>> -             unsigned int npages = nr_pages;
> >>> +             unsigned int nr_blocks = fi.length >> sbi->log_blocksize;
> >>
> >> F2FS_BYTES_TO_BLK(sbi, fi.length);
> >>
> >>>               enum count_type type;
> >>>
> >>>   #ifdef CONFIG_F2FS_FS_COMPRESSION
> >>> @@ -441,8 +440,7 @@ static void f2fs_write_end_bio(struct bio *bio)
> >>>                       }
> >>>               }
> >>>
> >>> -             while (nr_pages--)
> >>> -                     dec_cache_count(sbi, type);
> >>> +             sub_cache_counts(sbi, type, nr_blocks);
> >>>
> >>>               /*
> >>>                * we should access sbi before folio_end_writeback() to
> >>> @@ -452,7 +450,7 @@ static void f2fs_write_end_bio(struct bio *bio)
> >>>                               wq_has_sleeper(&sbi->cp_wait))
> >>>                       wake_up(&sbi->cp_wait);
> >>>
> >>> -             f2fs_ffs_put_write_pending(folio, npages);
> >>> +             f2fs_ffs_put_write_pending(folio, nr_blocks);
> >>>       }
> >>>
> >>>       bio_put(bio);
> >>> @@ -3023,7 +3021,7 @@ static void f2fs_clear_truncated_page_state(struct folio *folio, pgoff_t i)
> >>>   {
> >>>       struct f2fs_sb_info *sbi = F2FS_F_SB(folio);
> >>>
> >>> -     if (f2fs_folio_has_ffs(folio)) {
> >>> +     if (f2fs_is_multiblock_folio(sbi, folio)) {
> >>>               f2fs_ffs_clear_subrange_uptodate(folio,
> >>>                               F2FS_BLK_TO_BYTES(sbi, i), F2FS_BLKSIZE(sbi));
> >>>       } else {
> >>> @@ -3051,21 +3049,6 @@ bool f2fs_ffs_test_blk_dirty(const struct folio *folio, pgoff_t index)
> >>>       return test_bit(nr_blocks + offset, ffs->state);
> >>>   }
> >>>
> >>> -static unsigned int __ffs_mark_subrange_dirty(struct folio *folio,
> >>> -                     struct f2fs_folio_state *ffs, size_t offset, size_t len)
> >>> -{
> >>> -     struct f2fs_sb_info *sbi = F2FS_F_SB(folio);
> >>> -     unsigned int nr_blocks = f2fs_blocks_per_folio(sbi, folio);
> >>> -     unsigned int start, end, before;
> >>> -
> >>> -     start = F2FS_BYTES_TO_BLK(sbi, offset);
> >>> -     end = min_t(unsigned int, F2FS_BLK_ALIGN(sbi, offset + len), nr_blocks);
> >>> -
> >>> -     before = bitmap_weight(ffs->state, 2 * nr_blocks);
> >>> -     bitmap_set(ffs->state, nr_blocks + start, end - start);
> >>> -     return bitmap_weight(ffs->state, 2 * nr_blocks) - before;
> >>> -}
> >>> -
> >>>   /*
> >>>    * Mark the given range dirty for writeback.
> >>>    *
> >>> @@ -3078,7 +3061,8 @@ void f2fs_ffs_mark_subrange_dirty(struct folio *folio,
> >>>   {
> >>>       struct f2fs_sb_info *sbi = F2FS_F_SB(folio);
> >>>       struct f2fs_folio_state *ffs;
> >>> -     unsigned int set;
> >>> +     unsigned int nr_blocks;
> >>> +     unsigned int start, end;
> >>>       unsigned long flags;
> >>>
> >>>       f2fs_bug_on(F2FS_F_SB(folio), offset + len > folio_size(folio));
> >>> @@ -3087,13 +3071,13 @@ void f2fs_ffs_mark_subrange_dirty(struct folio *folio,
> >>>               return;
> >>>
> >>>       ffs = f2fs_ffs_find_or_alloc(folio);
> >>> +     nr_blocks = f2fs_blocks_per_folio(sbi, folio);
> >>> +     start = F2FS_BYTES_TO_BLK(sbi, offset);
> >>> +     end = min_t(unsigned int, F2FS_BLK_ALIGN(sbi, offset + len), nr_blocks);
> >>>
> >>>       spin_lock_irqsave(&ffs->state_lock, flags);
> >>> -     set = __ffs_mark_subrange_dirty(folio, ffs, offset, len);
> >>> +     bitmap_set(ffs->state, start + nr_blocks, end - start);
> >>>       spin_unlock_irqrestore(&ffs->state_lock, flags);
> >>> -
> >>> -     if (set)
> >>> -             f2fs_account_dirty_blocks(folio->mapping->host, set);
> >>>   }
> >>>
> >>>   void f2fs_ffs_clear_subrange_uptodate(struct folio *folio,
> >>> @@ -3129,19 +3113,16 @@ void f2fs_ffs_clear_subrange_uptodate(struct folio *folio,
> >>>   }
> >>>
> >>>   static bool __ffs_clear_subrange_dirty(struct folio *folio,
> >>> -                     struct f2fs_folio_state *ffs, size_t offset, size_t len,
> >>> -                     unsigned int *cleared)
> >>> +                     struct f2fs_folio_state *ffs, size_t offset, size_t len)
> >>>   {
> >>>       struct f2fs_sb_info *sbi = F2FS_F_SB(folio);
> >>>       unsigned int nr_blocks = f2fs_blocks_per_folio(sbi, folio);
> >>> -     unsigned int start, end, before;
> >>> +     unsigned int start, end;
> >>>
> >>>       start = F2FS_BYTES_TO_BLK(sbi, offset);
> >>>       end = min_t(unsigned int, F2FS_BLK_ALIGN(sbi, offset + len), nr_blocks);
> >>>
> >>> -     before = bitmap_weight(ffs->state, 2 * nr_blocks);
> >>>       bitmap_clear(ffs->state, nr_blocks + start, end - start);
> >>> -     *cleared = before - bitmap_weight(ffs->state, 2 * nr_blocks);
> >>>       return find_next_bit(ffs->state, 2 * nr_blocks, nr_blocks) <
> >>>                       2 * nr_blocks;
> >>>   }
> >>> @@ -3153,15 +3134,13 @@ static bool __ffs_clear_subrange_dirty(struct folio *folio,
> >>>    * @len: byte length of the subrange
> >>>    *
> >>>    * Clear the dirty bits of the 4K subpages covered by [offset, offset + len),
> >>> - * account the cleared subpages against the inode dirty counters, and return
> >>> - * whether the folio still has any dirty subpage left.
> >>> + * and return whether the folio still has any dirty subpage left.
> >>>    */
> >>>   bool f2fs_ffs_clear_subrange_dirty_and_test(struct folio *folio, size_t offset,
> >>>                                           size_t len)
> >>>   {
> >>>       struct f2fs_folio_state *ffs;
> >>>       unsigned long flags;
> >>> -     unsigned int cleared = 0;
> >>>       bool dirty;
> >>>
> >>>       if (!f2fs_folio_has_ffs(folio)) {
> >>> @@ -3178,12 +3157,9 @@ bool f2fs_ffs_clear_subrange_dirty_and_test(struct folio *folio, size_t offset,
> >>>
> >>>       ffs = f2fs_ffs_find_or_alloc(folio);
> >>>       spin_lock_irqsave(&ffs->state_lock, flags);
> >>> -     dirty = __ffs_clear_subrange_dirty(folio, ffs, offset, len, &cleared);
> >>> +     dirty = __ffs_clear_subrange_dirty(folio, ffs, offset, len);
> >>>       spin_unlock_irqrestore(&ffs->state_lock, flags);
> >>>
> >>> -     if (cleared)
> >>> -             f2fs_account_dirty_blocks(folio->mapping->host, -cleared);
> >>> -
> >>>       return dirty;
> >>>   }
> >>>
> >>> @@ -3943,7 +3919,7 @@ int f2fs_do_write_data_page(struct f2fs_io_info *fio)
> >>>   static int f2fs_write_folio_dirty_range(struct folio *folio, int *submitted,
> >>>                                       struct writeback_control *wbc,
> >>>                                       enum iostat_type io_type,
> >>> -                                     u64 *pos, u64 len)
> >>> +                                     u64 start, u64 end)
> >>>   {
> >>>       struct inode *inode = folio->mapping->host;
> >>>       struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >>> @@ -3951,19 +3927,19 @@ static int f2fs_write_folio_dirty_range(struct folio *folio, int *submitted,
> >>>                               folio_test_f2fs_atomic(folio);
> >>>       struct inode *dn_inode = atomic_commit ?
> >>>                               F2FS_I(inode)->cow_inode : inode;
> >>> -     struct f2fs_folio_state *ffs = NULL;
> >>> -     u64 folio_start = folio_pos(folio);
> >>> -     pgoff_t start_idx = (*pos - folio_start) >> PAGE_SHIFT;
> >>> -     pgoff_t end_idx = (*pos - folio_start + len - 1) >> PAGE_SHIFT;
> >>> +     u64 pos = folio_pos(folio);
> >>> +     pgoff_t start_idx = (start - pos) >> sbi->log_blocksize;
> >>> +     pgoff_t end_idx = (end - 1 - pos) >> sbi->log_blocksize;
> >>
> >> F2FS_BYTES_TO_BLK(sbi, start - pos);
> >> F2FS_BYTES_TO_BLK(sbi, end - 1 - pos);
> >>
> >>> +     pgoff_t last_idx = 0;
> >>> +     pgoff_t i;
> >>> +     int local_submitted = 0;
> >>>       int err = 0;
> >>>
> >>> -     for (pgoff_t i = start_idx; i <= end_idx && !err; i++) {
> >>> +     for (i = start_idx; i <= end_idx; i++) {
> >>>               struct dnode_of_data dn;
> >>>               struct node_info ni;
> >>> -             pgoff_t data_idx = folio->index + i;
> >>> +             pgoff_t data_idx = f2fs_folio_lblk(sbi, folio) + i;
> >>>               bool ipu_force = false;
> >>> -             bool dn_held = false;
> >>> -             bool submitted_blk = false;
> >>>               struct f2fs_io_info fio = {
> >>>                       .sbi = sbi,
> >>>                       .ino = inode->i_ino,
> >>> @@ -3983,7 +3959,12 @@ static int f2fs_write_folio_dirty_range(struct folio *folio, int *submitted,
> >>>               };
> >>>
> >>>               if (f2fs_folio_has_ffs(folio)) {
> >>> -                     ffs = (struct f2fs_folio_state *)folio->private;
> >>> +                     struct f2fs_folio_state *ffs =
> >>> +                             (struct f2fs_folio_state *)folio->private;
> >>> +
> >>> +                     /* Write only dirty blocks */
> >>> +                     if (!f2fs_ffs_test_blk_dirty(folio, data_idx))
> >>> +                             continue;
> >>>                       atomic_inc(&ffs->write_blocks_pending);
> >>>               }
> >>>
> >>> @@ -3995,7 +3976,7 @@ static int f2fs_write_folio_dirty_range(struct folio *folio, int *submitted,
> >>>                       if (!f2fs_is_valid_blkaddr(sbi, fio.old_blkaddr,
> >>>                                                  DATA_GENERIC_ENHANCE)) {
> >>>                               err = -EFSCORRUPTED;
> >>> -                             goto block_done;
> >>> +                             goto skip_block;
> >>>                       }
> >>>                       ipu_force = true;
> >>>                       goto got_it;
> >>> @@ -4015,24 +3996,22 @@ static int f2fs_write_folio_dirty_range(struct folio *folio, int *submitted,
> >>>                                                    LOOKUP_NODE);
> >>>               }
> >>>               if (err && err != -ENOENT)
> >>> -                     goto block_done;
> >>> -             dn_held = true;
> >>> +                     goto skip_block;
> >>>
> >>> -             fio.old_blkaddr = dn.data_blkaddr;
> >>> -
> >>> -             /* This page is already truncated */
> >>> -             if (err == -ENOENT || fio.old_blkaddr == NULL_ADDR) {
> >>> -                     f2fs_clear_truncated_page_state(folio, i);
> >>> +             /* This block is already truncated */
> >>> +             if (err || dn.data_blkaddr == NULL_ADDR) {
> >>>                       err = 0;
> >>> -                     goto block_done;
> >>> +                     f2fs_clear_truncated_page_state(folio, i);
> >>> +                     goto skip_block;
> >>>               }
> >>>
> >>> +             fio.old_blkaddr = dn.data_blkaddr;
> >>>   got_it:
> >>>               if (__is_valid_data_blkaddr(fio.old_blkaddr) &&
> >>>                   !f2fs_is_valid_blkaddr(sbi, fio.old_blkaddr,
> >>>                                          DATA_GENERIC_ENHANCE)) {
> >>>                       err = -EFSCORRUPTED;
> >>> -                     goto block_done;
> >>> +                     goto skip_block;
> >>>               }
> >>>
> >>>               if (fio.meta_gc)
> >>> @@ -4042,61 +4021,109 @@ static int f2fs_write_folio_dirty_range(struct folio *folio, int *submitted,
> >>>                   (__is_valid_data_blkaddr(fio.old_blkaddr) &&
> >>>                                           need_inplace_update(&fio))) {
> >>>                       f2fs_put_dnode(&dn);
> >>> -                     dn_held = false;
> >>>                       err = f2fs_inplace_write_data(&fio);
> >>> -                     trace_f2fs_do_write_data_page(folio, IPU);
> >>>                       if (err)
> >>> -                             goto block_done;
> >>> +                             goto skip_block_no_dnode;
> >>>
> >>> -                     if (submitted)
> >>> -                             (*submitted)++;
> >>> -                     submitted_blk = true;
> >>> +                     local_submitted++;
> >>> +                     last_idx = data_idx;
> >>>                       set_inode_flag(inode, FI_UPDATE_WRITE);
> >>> -                     goto block_done;
> >>> +                     trace_f2fs_do_write_data_page(folio, IPU);
> >>> +                     continue;
> >>>               }
> >>>
> >>>               err = f2fs_get_node_info(sbi, dn.nid, &ni, false);
> >>>               if (err)
> >>> -                     goto block_done;
> >>> +                     goto skip_block;
> >>>
> >>>               fio.version = ni.version;
> >>>
> >>>               f2fs_outplace_write_data(&dn, &fio);
> >>> -             /*
> >>> -              * The outplace write path failed to submit this block.
> >>> -              */
> >>> +             f2fs_put_dnode(&dn);
> >>> +             /* The outplace write path failed to submit this block. */
> >>>               if (!fio.submitted) {
> >>>                       err = -EIO;
> >>> -                     goto block_done;
> >>> +                     goto skip_block_no_dnode;
> >>>               }
> >>> -             if (submitted)
> >>> -                     (*submitted)++;
> >>> -             submitted_blk = true;
> >>> +             local_submitted++;
> >>> +             last_idx = data_idx;
> >>>               set_inode_flag(inode, FI_APPEND_WRITE);
> >>>               trace_f2fs_do_write_data_page(folio, OPU);
> >>> -block_done:
> >>> -             if (dn_held)
> >>> -                     f2fs_put_dnode(&dn);
> >>> +             continue;
> >>> +
> >>> +skip_block:
> >>> +             f2fs_put_dnode(&dn);
> >>> +skip_block_no_dnode:
> >>> +             if (f2fs_folio_has_ffs(folio))
> >>> +                     f2fs_ffs_put_write_pending(folio, 1);
> >>> +             if (err)
> >>> +                     break;
> >>> +     }
> >>> +
> >>> +     if (err) {
> >>>               /*
> >>> -              * If this block was not submitted, roll back its
> >>> -              * write pages pending.
> >>> +              * The blocks before the failed one were written or skipped, so
> >>> +              * keep only the failed block and the ones after it dirty.
> >>>                */
> >>> -             if (!submitted_blk && ffs)
> >>> -                     f2fs_ffs_put_write_pending(folio, 1);
> >>> -             if (!err) {
> >>> -                     *pos = ((loff_t)data_idx + 1) << PAGE_SHIFT;
> >>> -                     spin_lock(&F2FS_I(inode)->i_size_lock);
> >>> -                     if (F2FS_I(inode)->last_disk_size < *pos)
> >>> -                             F2FS_I(inode)->last_disk_size = *pos;
> >>> -                     spin_unlock(&F2FS_I(inode)->i_size_lock);
> >>> -             } else {
> >>> -                     file_set_keep_isize(inode);
> >>> +             if (i > start_idx) {
> >>> +                     size_t len = F2FS_BLK_TO_BYTES(sbi, i - start_idx);
> >>> +
> >>> +                     f2fs_ffs_clear_subrange_dirty_and_test(folio,
> >>> +                                                            start - pos, len);
> >>>               }
> >>> +             file_set_keep_isize(inode);
> >>> +     } else if (local_submitted) {
> >>> +             loff_t psize = (loff_t)(last_idx + 1) << sbi->log_blocksize;
> >>
> >> F2FS_BLK_TO_BYTES(sbi, last_idx + 1)
> >>
> >>> +
> >>> +             if (psize > i_size_read(inode))
> >>> +                     psize = i_size_read(inode);
> >>
> >> It seems an improvement, to avoid unnecessary inode write during fsync, can we fix
> >> f2fs_write_single_data_page as well? maybe it's better fix them all in a separated
> >> patch?
> >
> > Agreed. f2fs_write_single_data_page() and the compressed write path also
> > set last_disk_size beyond i_size. Besides the extra inode write, if
> > i_size grows to the recorded value later, f2fs_skip_inode_update() can
> > see last_disk_size == i_size even though the inode on disk still has
> > the old size. I will fix all of them in a separate patch.
> >
> >>
> >>> +
> >>> +             spin_lock(&F2FS_I(inode)->i_size_lock);
> >>> +             if (F2FS_I(inode)->last_disk_size < psize)
> >>> +                     F2FS_I(inode)->last_disk_size = psize;
> >>> +             spin_unlock(&F2FS_I(inode)->i_size_lock);
> >>>       }
> >>>
> >>> +     if (submitted)
> >>> +             *submitted = local_submitted;
> >>>       return err;
> >>>   }
> >>>
> >>> +/* Dentry and quota blocks are controlled by checkpoint. */
> >>> +static bool f2fs_cp_controlled_inode(struct inode *inode)
> >>> +{
> >>> +     return S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode);
> >>> +}
> >>> +
> >>> +enum f2fs_wb_action {
> >>> +     F2FS_WB_WRITE,          /* write back the folio */
> >>> +     F2FS_WB_REDIRTY,        /* keep the folio dirty */
> >>> +     F2FS_WB_DROP,           /* drop the dirty data */
> >>> +};
> >>> +
> >>> +/* Decide what to do with a dirty data folio before writing it back. */
> >>> +static enum f2fs_wb_action f2fs_wb_folio_action(struct f2fs_sb_info *sbi,
> >>> +                                             struct inode *inode)
> >>> +{
> >>> +     /* we should bypass data pages to proceed the kworker jobs */
> >>> +     if (unlikely(f2fs_cp_error(sbi))) {
> >>> +             mapping_set_error(inode->i_mapping, -EIO);
> >>> +             /*
> >>> +              * Keep dirty dentry folios for the latest directory structure,
> >>> +              * and keep data folios in remount-ro mode.
> >>> +              */
> >>> +             if ((S_ISDIR(inode->i_mode) &&
> >>> +                  !is_sbi_flag_set(sbi, SBI_IS_CLOSE)) ||
> >>> +                 F2FS_OPTION(sbi).errors == MOUNT_ERRORS_READONLY)
> >>> +                     return F2FS_WB_REDIRTY;
> >>> +             return F2FS_WB_DROP;
> >>> +     }
> >>> +
> >>> +     if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
> >>> +             return F2FS_WB_REDIRTY;
> >>> +     return F2FS_WB_WRITE;
> >>> +}
> >>> +
> >>>   int f2fs_write_single_data_page(struct folio *folio, int *submitted,
> >>>                               struct bio **bio,
> >>>                               sector_t *last_block,
> >>> @@ -4137,26 +4164,15 @@ int f2fs_write_single_data_page(struct folio *folio, int *submitted,
> >>>
> >>>       trace_f2fs_writepage(folio, DATA);
> >>>
> >>> -     /* we should bypass data pages to proceed the kworker jobs */
> >>> -     if (unlikely(f2fs_cp_error(sbi))) {
> >>> -             mapping_set_error(folio->mapping, -EIO);
> >>> -             /*
> >>> -              * don't drop any dirty dentry pages for keeping lastest
> >>> -              * directory structure.
> >>> -              */
> >>> -             if (S_ISDIR(inode->i_mode) &&
> >>> -                             !is_sbi_flag_set(sbi, SBI_IS_CLOSE))
> >>> -                     goto redirty_out;
> >>> -
> >>> -             /* keep data pages in remount-ro mode */
> >>> -             if (F2FS_OPTION(sbi).errors == MOUNT_ERRORS_READONLY)
> >>> -                     goto redirty_out;
> >>> +     switch (f2fs_wb_folio_action(sbi, inode)) {
> >>> +     case F2FS_WB_REDIRTY:
> >>> +             goto redirty_out;
> >>> +     case F2FS_WB_DROP:
> >>>               goto out;
> >>> +     case F2FS_WB_WRITE:
> >>> +             break;
> >>>       }
> >>>
> >>> -     if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
> >>> -             goto redirty_out;
> >>> -
> >>>       if (folio->index < end_index ||
> >>>                       f2fs_verity_in_progress(inode) ||
> >>>                       compr_blocks)
> >>> @@ -4172,8 +4188,7 @@ int f2fs_write_single_data_page(struct folio *folio, int *submitted,
> >>>
> >>>       folio_zero_segment(folio, offset, folio_size(folio));
> >>>   write:
> >>> -     /* Dentry/quota blocks are controlled by checkpoint */
> >>> -     if (S_ISDIR(inode->i_mode) || quota_inode) {
> >>> +     if (f2fs_cp_controlled_inode(inode)) {
> >>>               struct f2fs_lock_context lc;
> >>>
> >>>               /*
> >>> @@ -4224,14 +4239,14 @@ int f2fs_write_single_data_page(struct folio *folio, int *submitted,
> >>>               goto redirty_out;
> >>>
> >>>   out:
> >>> -     inode_dec_dirty_block(inode);
> >>> +     inode_sub_dirty_blocks(inode, f2fs_blocks_per_folio(sbi, folio));
> >>>       if (err) {
> >>>               folio_clear_uptodate(folio);
> >>>               folio_clear_f2fs_gcing(folio);
> >>>       }
> >>>       folio_unlock(folio);
> >>> -     if (!S_ISDIR(inode->i_mode) && !IS_NOQUOTA(inode) &&
> >>> -                     !F2FS_I(inode)->wb_task && allow_balance)
> >>> +     if (!f2fs_cp_controlled_inode(inode) &&
> >>> +         !F2FS_I(inode)->wb_task && allow_balance)
> >>>               f2fs_balance_fs(sbi, need_balance_fs);
> >>>
> >>>       if (unlikely(f2fs_cp_error(sbi))) {
> >>> @@ -4560,6 +4575,7 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>       int submitted = 0;
> >>>       int nwritten = 0;
> >>>       bool op_locked = false;
> >>> +     bool node_locked = false;
> >>>       bool retry = false;
> >>>
> >>>       if (get_dirty_blocks(inode) <= SM_I(sbi)->min_hot_blocks)
> >>> @@ -4571,20 +4587,15 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>               struct f2fs_folio_state *ffs = NULL;
> >>>               u64 isize;
> >>>               size_t poff;
> >>> -             size_t clear_len;
> >>>               pgoff_t end_index;
> >>>               bool verity_in_progress;
> >>>               int folio_submitted = 0;
> >>>               bool bias_added = false;
> >>>
> >>>               submitted = 0;
> >>> +             err = 0;
> >>>               retry = false;
> >>>
> >>> -             if (err) {
> >>> -                     folio_redirty_for_writepage(wbc, folio);
> >>> -                     goto retry_out;
> >>> -             }
> >>> -
> >>>               if (atomic_read(&sbi->wb_sync_req[DATA]) &&
> >>>                   wbc->sync_mode == WB_SYNC_NONE) {
> >>>                       folio_redirty_for_writepage(wbc, folio);
> >>> @@ -4597,11 +4608,22 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>                       goto retry_out;
> >>>               }
> >>>
> >>> +             if (f2fs_has_subpage_blocks(sbi) &&
> >>> +                 (f2fs_compressed_file(inode) || f2fs_is_atomic_file(inode))) {
> >>> +                     WARN_ON_ONCE(1);
> >>> +                     mapping_set_error(mapping, -EOPNOTSUPP);
> >>> +                     folio_clear_dirty_for_io(folio);
> >>> +                     inode_sub_dirty_blocks(inode, f2fs_blocks_per_folio(sbi, folio));
> >>> +                     err = -EOPNOTSUPP;
> >>> +                     goto retry_out;
> >>> +             }
> >>> +
> >>>               /*
> >>>                * Writing back one large folio performs multiple block allocations, so
> >>>                * best-effort balance the filesystem before writing it back.
> >>>                */
> >>> -             if (!F2FS_I(inode)->wb_task && has_not_enough_free_secs(sbi, 0, 0)) {
> >>> +             if (!f2fs_cp_controlled_inode(inode) &&
> >>> +                 !F2FS_I(inode)->wb_task && has_not_enough_free_secs(sbi, 0, 0)) {
> >>>                       folio_redirty_for_writepage(wbc, folio);
> >>>                       retry = true;
> >>>                       folio_unlock(folio);
> >>> @@ -4636,31 +4658,39 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>               }
> >>>
> >>>               /*
> >>> -              * If cp_error is set, all subpages of this folio are not
> >>> -              * written back unless the filesystem is mounted with
> >>> -              * errors=remount-ro.  The check is placed after the retry
> >>> -              * block so it also covers cp_error being set while the folio
> >>> -              * lock was dropped for f2fs_balance_fs() or for the trylock_op()
> >>> -              * backoff.  PG_dirty is clear at this point, so both the
> >>> -              * redirty and the drop below leave a coherent state.
> >>> +              * Checked after the retry block, so that it also covers cp_error
> >>> +              * being set while the folio lock was dropped for f2fs_balance_fs()
> >>> +              * or for the trylock_op() backoff.
> >>>                */
> >>> -             if (unlikely(f2fs_cp_error(sbi))) {
> >>> -                     mapping_set_error(mapping, -EIO);
> >>> -                     if (F2FS_OPTION(sbi).errors == MOUNT_ERRORS_READONLY) {
> >>> -                             folio_redirty_for_writepage(wbc, folio);
> >>> -                             goto retry_out;
> >>> -                     }
> >>> -                     goto out;
> >>> +             switch (f2fs_wb_folio_action(sbi, inode)) {
> >>> +             case F2FS_WB_REDIRTY:
> >>> +                     folio_redirty_for_writepage(wbc, folio);
> >>> +                     goto retry_out;
> >>> +             case F2FS_WB_DROP:
> >>> +                     f2fs_ffs_clear_subrange_dirty_and_test(folio, 0,
> >>> +                                             folio_size(folio));
> >>> +                     inode_sub_dirty_blocks(inode, f2fs_blocks_per_folio(sbi, folio));
> >>> +                     goto retry_out;
> >>> +             case F2FS_WB_WRITE:
> >>> +                     break;
> >>>               }
> >>>
> >>> -             /* To avoid dealing with the complexity for one subrange is in bio
> >>> -              * while we trylock_op failed before writing another subrange.
> >>> -              * Try to lock_op before any subrange write for the folio.
> >>> -              */
> >>> -             if (!op_locked) {
> >>> +             if (f2fs_cp_controlled_inode(inode)) {
> >>> +                     /*
> >>> +                      * Quota writes need node_write to avoid block
> >>> +                      * allocation during checkpoint.
> >>> +                      */
> >>> +                     if (IS_NOQUOTA(inode)) {
> >>> +                             f2fs_down_read_trace(&sbi->node_write, &lc);
> >>> +                             node_locked = true;
> >>> +                     }
> >>> +             } else {
> >>> +                     /* To avoid dealing with the complexity for one subrange is in bio
> >>> +                      * while we trylock_op failed before writing another subrange.
> >>> +                      * Try to lock_op before any subrange write for the folio.
> >>> +                      */
> >>>                       if (!f2fs_trylock_op(sbi, &lc)) {
> >>>                               folio_redirty_for_writepage(wbc, folio);
> >>> -                             err = 0;
> >>>                               if (wbc->sync_mode != WB_SYNC_ALL)
> >>>                                       goto retry_out;
> >>>
> >>> @@ -4690,59 +4720,34 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>               folio_start_writeback(folio);
> >>>
> >>>               /*
> >>> -              * PG_dirty was already cleared by writeback_iter(), and a
> >>> -              * single-block folio has no ffs dirty bitmap, so the dirty
> >>> -              * range cannot be derived. Write the whole folio.
> >>> +              * PG_dirty was already cleared by writeback_iter(). A single-block
> >>> +              * folio has no ffs, so its whole folio is written.
> >>>                */
> >>> -             if (!folio_test_large(folio)) {
> >>> -                     err = f2fs_write_folio_dirty_range(folio, &submitted,
> >>> -                                     wbc, io_type, &pos, end_pos - pos);
> >>> -                     folio_submitted += submitted;
> >>> -                     if (err)
> >>> -                             goto out;
> >>> -                     nwritten += submitted;
> >>> -                     goto written;
> >>> -             }
> >>> -
> >>> -             if (!f2fs_folio_has_ffs(folio)) {
> >>> -                     ffs = f2fs_ffs_find_or_alloc(folio);
> >>> -                     f2fs_ffs_mark_subrange_dirty(folio, 0, end_pos - pos);
> >>> -             } else {
> >>> +             if (f2fs_is_multiblock_folio(sbi, folio)) {
> >>> +                     if (!f2fs_folio_has_ffs(folio))
> >>> +                             f2fs_ffs_mark_subrange_dirty(folio, 0, end_pos - pos);
> >>>                       ffs = (struct f2fs_folio_state *)folio->private;
> >>> +                     /*
> >>> +                      * Multiblock folios can be submitted as multiple bios,
> >>> +                      * which may complete while we are still submitting the
> >>> +                      * remaining dirty ranges.  Hold a bias on
> >>> +                      * write_blocks_pending to prevent folio_end_writeback()
> >>> +                      * from being called early.
> >>> +                      */
> >>> +                     if (!bias_added) {
> >>> +                             WARN_ON_ONCE(atomic_read(&ffs->write_blocks_pending) != 0);
> >>> +                             atomic_inc(&ffs->write_blocks_pending);
> >>> +                             bias_added = true;
> >>> +                     }
> >>>               }
> >>> -             /*
> >>> -              * Large folios can be submitted as multiple bios, which may
> >>> -              * complete while we are still submitting the remaining dirty
> >>> -              * ranges.  Hold a bias on write_blocks_pending to prevent
> >>> -              * folio_end_writeback() from being called early.
> >>> -              */
> >>> -             if (f2fs_folio_has_ffs(folio) && !bias_added) {
> >>> -                     WARN_ON_ONCE(atomic_read(&ffs->write_blocks_pending) != 0);
> >>> -                     atomic_inc(&ffs->write_blocks_pending);
> >>> -                     bias_added = true;
> >>> -             }
> >>> -
> >>> -             unsigned int from = 0, start, count;
> >>> -             unsigned int nr_blocks = f2fs_blocks_per_folio(sbi, folio);
> >>> -             unsigned int to_blk = min_t(unsigned int,
> >>> -                             F2FS_BLK_ALIGN(sbi, end_pos - folio_pos(folio)),
> >>> -                             nr_blocks);
> >>>
> >>> -             while (f2fs_ffs_dirty_blk_range(folio, from, to_blk,
> >>> -                                             &start, &count)) {
> >>> -                     submitted = 0;
> >>> -                     pos = folio_pos(folio) + F2FS_BLK_TO_BYTES(sbi, start);
> >>> -                     err = f2fs_write_folio_dirty_range(folio, &submitted,
> >>> -                                     wbc, io_type, &pos,
> >>> -                                     F2FS_BLK_TO_BYTES(sbi, count));
> >>> -                     folio_submitted += submitted;
> >>> -                     nwritten += submitted;
> >>> -                     if (err)
> >>> -                             goto out;
> >>> -                     from = start + count;
> >>> -             }
> >>> +             err = f2fs_write_folio_dirty_range(folio, &submitted, wbc, io_type,
> >>> +                                                pos, end_pos);
> >>> +             folio_submitted += submitted;
> >>> +             nwritten += submitted;
> >>> +             if (err)
> >>> +                     goto out;
> >>>
> >>> -written:
> >>>               /* If none of the subpages of a folio is submitted, keep the atomic flag */
> >>>               if (folio_submitted &&
> >>>                   f2fs_is_atomic_file(inode) &&
> >>> @@ -4750,26 +4755,12 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>                       folio_clear_f2fs_atomic(folio);
> >>>
> >>>   out:
> >>> -             /*
> >>> -              * Clear the dirty state of the subranges that were written back.
> >>> -              * If some subranges are still dirty (e.g. the folio was only
> >>> -              * partially written back), or if the writeback failed, the
> >>> -              * folio must stay dirty so that the remaining subranges are
> >>> -              * written back later.
> >>> -              *
> >>> -              * On success, clear dirty bits of the whole folio rather than
> >>> -              * up to isize: subpages beyond EOF can still carry dirty bits
> >>> -              * (e.g. fill_zero() w/ FALLOC_FL_KEEP_SIZE, BG_GC on blocks
> >>> -              * beyond EOF, or f2fs_ffs_find_or_alloc() on a dirty folio),
> >>> -              * they will never be written back, and would keep the folio
> >>> -              * redirtied forever.
> >>> -              */
> >>> -             clear_len = err ? pos - folio_pos(folio) : folio_size(folio);
> >>> -             if (f2fs_ffs_clear_subrange_dirty_and_test(folio, 0,
> >>> -                                             clear_len) || err) {
> >>> +             if (!err) {
> >>> +                     f2fs_ffs_clear_subrange_dirty_and_test(folio, 0,
> >>> +                                             folio_size(folio));
> >>> +                     inode_sub_dirty_blocks(inode, f2fs_blocks_per_folio(sbi, folio));
> >>> +             } else {
> >>>                       folio_redirty_for_writepage(wbc, folio);
> >>> -             } else if (!f2fs_folio_has_ffs(folio)) {
> >>> -                     inode_dec_dirty_block(inode);
> >>>               }
> >>>
> >>>               /*
> >>> @@ -4780,7 +4771,7 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>                       f2fs_ffs_put_write_pending(folio, 1);
> >>>               } else if (!folio_submitted && folio_test_writeback(folio)) {
> >>>                       /*
> >>> -                      * Order-0 folios take no bias, so end the writeback
> >>> +                      * Single-block folios take no bias, so end the writeback
> >>>                        * if nothing was submitted.
> >>>                        */
> >>>                       folio_end_writeback(folio);
> >>> @@ -4792,6 +4783,11 @@ static int f2fs_write_cache_folios(struct address_space *mapping,
> >>>                       op_locked = false;
> >>>               }
> >>>
> >>> +             if (node_locked) {
> >>> +                     f2fs_up_read_trace(&sbi->node_write, &lc);
> >>> +                     node_locked = false;
> >>> +             }
> >>> +
> >>>               folio_unlock(folio);
> >>>       }
> >>>
> >>> @@ -4872,10 +4868,10 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
> >>>       if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
> >>>               goto skip_write;
> >>>
> >>> -     if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
> >>> -                     wbc->sync_mode == WB_SYNC_NONE &&
> >>> -                     get_dirty_blocks(inode) < nr_caches_to_skip(sbi, DATA) &&
> >>> -                     f2fs_available_free_memory(sbi, DIRTY_DENTS))
> >>> +     if (f2fs_cp_controlled_inode(inode) &&
> >>> +         wbc->sync_mode == WB_SYNC_NONE &&
> >>> +         get_dirty_blocks(inode) < nr_caches_to_skip(sbi, DATA) &&
> >>> +         f2fs_available_free_memory(sbi, DIRTY_DENTS))
> >>>               goto skip_write;
> >>>
> >>>       /* skip writing in file defragment preparing stage */
> >>> @@ -4902,7 +4898,7 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
> >>>       account_writeback(inode, true);
> >>>
> >>>       blk_start_plug(&plug);
> >>> -     if (mapping_large_folio_support(inode->i_mapping) &&
> >>> +     if (f2fs_has_multiblock_folios(inode) &&
> >>>           !f2fs_has_inline_data(inode))
> >>>               ret = f2fs_write_cache_folios(mapping, wbc, io_type);
> >>>       else
> >>> @@ -5136,7 +5132,7 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
> >>>       int err = 0;
> >>>       block_t ori_blk_addr = NULL_ADDR;
> >>>       bool cow_has_reserved_block = false;
> >>> -     bool append = ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode);
> >>> +     bool append = F2FS_BLK_TO_BYTES(sbi, index) >= i_size_read(inode);
> >>>
> >>>       /*
> >>>        * On the first attempt, an append write can skip the COW lookup and
> >>> @@ -5226,7 +5222,7 @@ static bool f2fs_balance_fs_folio_locked(struct folio *folio,
> >>>
> >>>   static int prepare_large_folio_write_begin(struct inode *inode,
> >>>                                         struct folio *folio, loff_t pos,
> >>> -                                       unsigned int len)
> >>> +                                       unsigned int len, bool *need_balance)
> >>>   {
> >>>       struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >>>       struct f2fs_folio_state *ffs;
> >>> @@ -5234,9 +5230,13 @@ static int prepare_large_folio_write_begin(struct inode *inode,
> >>>       size_t need_off = ori_off;
> >>>       int err = 0;
> >>>
> >>> +     if (f2fs_has_subpage_blocks(sbi) &&
> >>> +         (f2fs_compressed_file(inode) || f2fs_is_atomic_file(inode)))
> >>> +             return -EOPNOTSUPP;
> >>> +
> >>>       /*
> >>> -      * when the write did not come through f2fs_write_iter, we preallocate all
> >>> -      * blocks in the write range here.
> >>> +      * Reserve blocks without f2fs_balance_fs() since the folio is locked;
> >>> +      * the caller balances after unlocking it if *need_balance is set.
> >>
> >> I think there is potential risk if we don't allow unlock -> f2fs_balance_fs, e.g.
> >> multiple threads call write_begin to write high order large folio concurrently will
> >> consume free blocks quickly, it may run out of free segments potentially w/o fggc.
> >> thoughts?
> >
> > f2fs_balance_fs() is still called. f2fs_write_begin() calls
> > f2fs_balance_fs_folio_locked() right after this, which unlocks the
> > folio, calls f2fs_balance_fs() and locks it again, under the same
> > condition (node_changed) as before. It is only moved to the caller, so
> > that the order-0 and multi-block paths balance in one place. I will
> > make the comment clearer in v2.
>
> Actually, what I meant is it changed
> from a. one f2fs_balance_fs() after one __reserve_data_block()
> to b. one f2fs_balance_fs() after in-batch __reserve_data_block()
>
> So in high order large folio, in prepare_large_folio_write_begin() we may reserve
> hundreds of blocks, and then a following f2fs_balance_fs(), which may be late,
> especially in a small size image, mutliple threads write high order folio concurrently,
> it may run out of free section, due to we missed to call f2fs_balance_fs() in time?
>
> Thanks,
>

I see, you're right. It was changed because f2fs_vm_page_mkwrite() also
calls prepare_large_folio_write_begin() with subpage blocks, and it can
neither unlock the folio nor return -EAGAIN there. It calls
f2fs_balance_fs() before locking the folio, as before.

But there is no reason to change it for write_begin. In v2, I'll call
f2fs_balance_fs_folio_locked() after each __reserve_data_block() again when
it is called from f2fs_write_begin(), and skip it only for page_mkwrite.

Thanks,

> >
> > Thanks,
> >
> >>
> >> Thanks,
> >>
> >>>        */
> >>>       if (!is_inode_flag_set(inode, FI_PREALLOCATED_ALL) &&
> >>>           !IS_DEVICE_ALIASING(inode)) {
> >>> @@ -5252,9 +5252,7 @@ static int prepare_large_folio_write_begin(struct inode *inode,
> >>>                                                  &node_changed);
> >>>                       if (err)
> >>>                               return err;
> >>> -                     if (f2fs_balance_fs_folio_locked(folio, folio->mapping,
> >>> -                                                node_changed))
> >>> -                             return -EAGAIN;
> >>> +                     *need_balance |= node_changed;
> >>>               }
> >>>       }
> >>>
> >>> @@ -5266,8 +5264,12 @@ static int prepare_large_folio_write_begin(struct inode *inode,
> >>>       if (folio_test_uptodate(folio) || len == folio_size(folio))
> >>>               return 0;
> >>>
> >>> +     /*
> >>> +      * Skip read if the write starts at a block boundary and reaches EOF,
> >>> +      * and zero the rest of the folio instead.
> >>> +      */
> >>>       if (!f2fs_verity_in_progress(inode) &&
> >>> -         !(pos & (PAGE_SIZE - 1)) && (pos + len) >= i_size_read(inode)) {
> >>> +         !(pos & (F2FS_BLKSIZE(sbi) - 1)) && (pos + len) >= i_size_read(inode)) {
> >>>               size_t zoff = ori_off + len;
> >>>
> >>>               if (zoff < folio_size(folio))
> >>> @@ -5281,7 +5283,8 @@ static int prepare_large_folio_write_begin(struct inode *inode,
> >>>       while (find_next_valid_block(folio, ori_off,
> >>>                                    &need_off, len)) {
> >>>               struct dnode_of_data dn;
> >>> -             pgoff_t index = folio->index + (need_off >> PAGE_SHIFT);
> >>> +             pgoff_t index = f2fs_folio_lblk(sbi, folio) +
> >>> +                             F2FS_BYTES_TO_BLK(sbi, need_off);
> >>>               block_t blkaddr;
> >>>
> >>>               if (!f2fs_lookup_read_extent_cache_block(inode, index,
> >>> @@ -5297,12 +5300,13 @@ static int prepare_large_folio_write_begin(struct inode *inode,
> >>>                       f2fs_put_dnode(&dn);
> >>>
> >>>                       if (blkaddr == NEW_ADDR) {
> >>> -                             size_t off = offset_in_folio(folio,
> >>> -                                                          (loff_t)index << PAGE_SHIFT);
> >>> +                             size_t off = f2fs_folio_byte_offset(sbi,
> >>> +                                                             folio, index);
> >>>
> >>> -                             folio_zero_segment(folio, off, off + PAGE_SIZE);
> >>> +                             folio_zero_segment(folio, off,
> >>> +                                                off + F2FS_BLKSIZE(sbi));
> >>>                               f2fs_ffs_mark_subrange_uptodate(folio, off,
> >>> -                                                            PAGE_SIZE);
> >>> +                                                            F2FS_BLKSIZE(sbi));
> >>>                               continue;
> >>>                       }
> >>>               }
> >>> @@ -5401,12 +5405,18 @@ static int f2fs_write_begin(const struct kiocb *iocb,
> >>>               goto fail;
> >>>       }
> >>>
> >>> +     if (f2fs_has_subpage_blocks(sbi) &&
> >>> +         (f2fs_compressed_file(inode) || f2fs_is_atomic_file(inode))) {
> >>> +             err = -EOPNOTSUPP;
> >>> +             goto fail;
> >>> +     }
> >>> +
> >>>       /*
> >>>        * We should check this at this moment to avoid deadlock on inode page
> >>>        * and #0 page. The locking rule for inline_data conversion should be:
> >>>        * folio_lock(folio #0) -> folio_lock(inode_page)
> >>>        */
> >>> -     if (index != 0) {
> >>> +     if (index != 0 || f2fs_has_subpage_blocks(sbi)) {
> >>>               err = f2fs_convert_inline_inode(inode);
> >>>               if (err)
> >>>                       goto fail;
> >>> @@ -5469,17 +5479,19 @@ static int f2fs_write_begin(const struct kiocb *iocb,
> >>>        */
> >>>       f2fs_folio_wait_writeback(folio, false, true);
> >>>
> >>> -     if (f2fs_is_atomic_file(inode) && !folio_test_large(folio))
> >>> +     if (f2fs_is_atomic_file(inode) && !f2fs_is_multiblock_folio(sbi, folio)) {
> >>>               err = prepare_atomic_write_begin(sbi, inode, folio->index,
> >>>                                       &blkaddr, &need_balance, retried);
> >>> -     else if (!folio_test_large(folio))
> >>> +     } else if (!f2fs_is_multiblock_folio(sbi, folio)) {
> >>>               err = prepare_write_begin(sbi, folio, pos, blen,
> >>>                                       &blkaddr, &need_balance);
> >>> -     else if (f2fs_is_atomic_file(inode))
> >>> +     } else if (f2fs_is_atomic_file(inode)) {
> >>>               err = prepare_large_folio_atomic_write_begin(inode,
> >>>                                       mapping, folio, pos, len, retried);
> >>> -     else
> >>> -             err = prepare_large_folio_write_begin(inode, folio, pos, blen);
> >>> +     } else {
> >>> +             err = prepare_large_folio_write_begin(inode, folio, pos, blen,
> >>> +                                                   &need_balance);
> >>> +     }
> >>>       if (err) {
> >>>               if (err == -EAGAIN) {
> >>>                       retried = true;
> >>> @@ -5495,7 +5507,7 @@ static int f2fs_write_begin(const struct kiocb *iocb,
> >>>               goto repeat;
> >>>       }
> >>>
> >>> -     if (folio_test_large(folio))
> >>> +     if (f2fs_is_multiblock_folio(sbi, folio))
> >>>               return 0;
> >>>
> >>>       if (blen == folio_size(folio) || folio_test_uptodate(folio))
> >>> @@ -5565,7 +5577,7 @@ static int f2fs_write_end(const struct kiocb *iocb,
> >>>       if (!folio_test_uptodate(folio)) {
> >>>               if (unlikely(copied != len)) {
> >>>                       copied = 0;
> >>> -             } else if (folio_test_large(folio)) {
> >>> +             } else if (f2fs_is_multiblock_folio(F2FS_I_SB(inode), folio)) {
> >>>                       f2fs_ffs_mark_subrange_uptodate(folio,
> >>>                                       offset_in_folio(folio, pos), len);
> >>>               } else {
> >>> @@ -5590,7 +5602,7 @@ static int f2fs_write_end(const struct kiocb *iocb,
> >>>       if (!copied)
> >>>               goto unlock_out;
> >>>
> >>> -     if (folio_test_large(folio))
> >>> +     if (f2fs_is_multiblock_folio(F2FS_I_SB(inode), folio))
> >>>               f2fs_ffs_mark_subrange_dirty(folio, offset_in_folio(folio, pos),
> >>>                                                                  copied);
> >>>       folio_mark_dirty(folio);
> >>> @@ -5642,6 +5654,9 @@ void f2fs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
> >>>                * dirty state.
> >>>                */
> >>>               if (!dirty && folio_test_dirty(folio)) {
> >>> +                     inode_sub_dirty_blocks(inode,
> >>> +                                     f2fs_blocks_per_folio(sbi, folio));
> >>> +                     f2fs_remove_dirty_inode(inode);
> >>>                       f2fs_clear_page_cache_dirty_tag(folio);
> >>>                       folio_cancel_dirty(folio);
> >>>               }
> >>> @@ -5650,11 +5665,8 @@ void f2fs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
> >>>               return;
> >>>       }
> >>>
> >>> -     if (f2fs_folio_has_ffs(folio)) {
> >>> -             f2fs_ffs_clear_subrange_dirty_and_test(folio, 0,
> >>> -                                                     folio_size(folio));
> >>> -     } else if (folio_test_dirty(folio)) {
> >>> -             inode_dec_dirty_block(inode);
> >>> +     if (folio_test_dirty(folio)) {
> >>> +             inode_sub_dirty_blocks(inode, f2fs_blocks_per_folio(sbi, folio));
> >>>               f2fs_remove_dirty_inode(inode);
> >>>       }
> >>>
> >>> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> >>> index aa3511c6f8fe..7f5dc2354a27 100644
> >>> --- a/fs/f2fs/dir.c
> >>> +++ b/fs/f2fs/dir.c
> >>> @@ -979,9 +979,9 @@ void f2fs_delete_entry(struct f2fs_dir_entry *dentry, void *dentry_block,
> >>>               if (!f2fs_has_subpage_blocks(sbi)) {
> >>>                       folio_clear_uptodate(folio);
> >>>                       folio_detach_private(folio);
> >>> -                     inode_dec_dirty_block(dir);
> >>>               }
> >>>
> >>> +             inode_sub_dirty_blocks(dir, f2fs_blocks_per_folio(sbi, folio));
> >>>               f2fs_remove_dirty_inode(dir);
> >>>       }
> >>>   keep_dirty:
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index cf7294068415..aab1095ad5ff 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -4457,7 +4457,6 @@ void f2fs_remove_orphan_inode(struct f2fs_sb_info *sbi, nid_t ino);
> >>>   int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi);
> >>>   int f2fs_get_valid_checkpoint(struct f2fs_sb_info *sbi);
> >>>   void f2fs_update_dirty_folio(struct inode *inode, struct folio *folio);
> >>> -void f2fs_account_dirty_blocks(struct inode *inode, int nr);
> >>>   void f2fs_remove_dirty_inode(struct inode *inode);
> >>>   int f2fs_sync_dirty_inodes(struct f2fs_sb_info *sbi, enum inode_type type,
> >>>                                                               bool from_cp);
> >>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >>> index 1ce4553b1d01..be548f39e33e 100644
> >>> --- a/fs/f2fs/file.c
> >>> +++ b/fs/f2fs/file.c
> >>> @@ -5561,12 +5561,13 @@ static int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *iter,
> >>>                       return ret;
> >>>       }
> >>>
> >>> -     if (!dio && mapping_large_folio_support(inode->i_mapping)) {
> >>> +     if (!dio && f2fs_has_multiblock_folios(inode)) {
> >>>               /*
> >>> -              * Preallocate all blocks touched by a large-folio buffered write so
> >>> -              * the regular write_begin path does not need to unlock the folio for
> >>> -              * f2fs_balance_fs().  Rechecking large-folio state after unlock is
> >>> -              * unreliable since partial truncation can split the folio.
> >>> +              * Preallocate all blocks touched by a multiblock-folio buffered
> >>> +              * write so the regular write_begin path does not need to unlock
> >>> +              * the folio for f2fs_balance_fs().  Rechecking large-folio
> >>> +              * state after unlock is unreliable since partial truncation can
> >>> +              * split the folio.
> >>>                */
> >>>               map.m_lblk = F2FS_BYTES_TO_BLK(sbi, pos);
> >>>               map.m_len = F2FS_BLK_ALIGN(sbi, pos + count);
> >>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>> index 6c24001325b2..f041a036836e 100644
> >>> --- a/fs/f2fs/gc.c
> >>> +++ b/fs/f2fs/gc.c
> >>> @@ -1608,13 +1608,12 @@ static int move_data_cache_block(struct inode *inode, block_t bidx, int gc_type,
> >>>                       f2fs_ffs_mark_subrange_dirty(folio, foff, F2FS_BLKSIZE(sbi));
> >>>               folio_mark_dirty(folio);
> >>>               if (folio_clear_dirty_for_io(folio)) {
> >>> -                     if (!has_ffs) {
> >>> -                             inode_dec_dirty_block(inode);
> >>> -                             f2fs_remove_dirty_inode(inode);
> >>> -                     } else if (f2fs_ffs_clear_subrange_dirty_and_test(folio,
> >>> -                                             foff, F2FS_BLKSIZE(sbi))) {
> >>> +                     inode_sub_dirty_blocks(inode, f2fs_blocks_per_folio(sbi, folio));
> >>> +                     f2fs_remove_dirty_inode(inode);
> >>> +                     if (has_ffs &&
> >>> +                         f2fs_ffs_clear_subrange_dirty_and_test(folio, foff,
> >>> +                                                     F2FS_BLKSIZE(sbi)))
> >>>                               folio_mark_dirty(folio);
> >>> -                     }
> >>>               }
> >>>
> >>>               folio_set_f2fs_gcing(folio);
> >>> diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
> >>> index ba0aff8e5643..757be9f8d069 100644
> >>> --- a/fs/f2fs/inline.c
> >>> +++ b/fs/f2fs/inline.c
> >>> @@ -196,10 +196,15 @@ int f2fs_convert_inline_folio(struct dnode_of_data *dn, struct folio *folio)
> >>>       folio_start_writeback(folio);
> >>>       fio.old_blkaddr = dn->data_blkaddr;
> >>>       set_inode_flag(dn->inode, FI_HOT_DATA);
> >>> +     if (f2fs_is_multiblock_folio(fio.sbi, folio)) {
> >>> +             struct f2fs_folio_state *ffs = f2fs_ffs_find_or_alloc(folio);
> >>> +
> >>> +             atomic_inc(&ffs->write_blocks_pending);
> >>> +     }
> >>>       f2fs_outplace_write_data(dn, &fio);
> >>>       f2fs_folio_wait_writeback(folio, true, true);
> >>>       if (dirty) {
> >>> -             inode_dec_dirty_block(dn->inode);
> >>> +             inode_sub_dirty_blocks(dn->inode, f2fs_blocks_per_folio(fio.sbi, folio));
> >>>               f2fs_remove_dirty_inode(dn->inode);
> >>>       }
> >>>
> >>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> >>> index c48b12208e20..b95bb5c27b0b 100644
> >>> --- a/fs/f2fs/node.c
> >>> +++ b/fs/f2fs/node.c
> >>> @@ -1700,7 +1700,7 @@ static void flush_inline_data(struct f2fs_sb_info *sbi, nid_t ino)
> >>>               goto folio_out;
> >>>
> >>>       ret = f2fs_write_inline_data(inode, folio);
> >>> -     inode_dec_dirty_block(inode);
> >>> +     inode_sub_dirty_blocks(inode, f2fs_blocks_per_folio(sbi, folio));
> >>>       f2fs_remove_dirty_inode(inode);
> >>>       if (ret)
> >>>               folio_mark_dirty(folio);
> >>
>