Re: [f2fs-dev] [PATCH v2] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc

From: Jaegeuk Kim
Date: Sun Aug 05 2018 - 12:08:50 EST

On 08/05, Chao Yu wrote:
> On 2018/8/5 6:29, Jaegeuk Kim wrote:
> > The f2fs_gc() called by f2fs_balance_fs() requires to be called outside of
> > fi->i_gc_rwsem[WRITE], since f2fs_gc() can try to grab it in a loop.
> >
> > If it hits the miximum retrials in GC, let's give a chance to release
> > gc_mutex for a short time in order not to go into live lock in the worst
> > case.
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > ---
> > v2 log from v1:
> > - keep lock order: i_gc_rwsem -> lock_op
> >
> > fs/f2fs/f2fs.h | 1 +
> > fs/f2fs/file.c | 76 ++++++++++++++++++++++++-----------------------
> > fs/f2fs/gc.c | 22 ++++++++++----
> > fs/f2fs/segment.c | 5 +++-
> > fs/f2fs/segment.h | 2 +-
> > 5 files changed, 61 insertions(+), 45 deletions(-)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index a9447c7d6570..50349780001b 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1223,6 +1223,7 @@ struct f2fs_sb_info {
> > unsigned int gc_mode; /* current GC state */
> > /* for skip statistic */
> > unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
> > + unsigned long long skipped_gc_rwsem; /* FG_GC only */
> >
> > /* threshold for gc trials on pinned files */
> > u64 gc_pin_file_threshold;
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 78c1bd6b8497..7bcf47f41ef1 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -1179,25 +1179,31 @@ static int __exchange_data_block(struct inode *src_inode,
> > return ret;
> > }
> >
> > -static int f2fs_do_collapse(struct inode *inode, pgoff_t start, pgoff_t end)
> > +static int f2fs_do_collapse(struct inode *inode, loff_t offset, loff_t len)
> > {
> > struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> > pgoff_t nrpages = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
> > + pgoff_t start = offset >> PAGE_SHIFT;
> > + pgoff_t end = (offset + len) >> PAGE_SHIFT;
> > int ret;
> >
> > f2fs_balance_fs(sbi, true);
> > - f2fs_lock_op(sbi);
> >
> > - f2fs_drop_extent_tree(inode);
> > + /* avoid gc operation during block exchange */
> > + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >
> > + f2fs_lock_op(sbi);
> > + f2fs_drop_extent_tree(inode);
> > + truncate_pagecache(inode, offset);
> > ret = __exchange_data_block(inode, inode, end, start, nrpages - end, true);
> > f2fs_unlock_op(sbi);
> > +
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > return ret;
> > }
> >
> > static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> > {
> > - pgoff_t pg_start, pg_end;
> > loff_t new_size;
> > int ret;
> >
> > @@ -1212,21 +1218,13 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> > if (ret)
> > return ret;
> >
> > - pg_start = offset >> PAGE_SHIFT;
> > - pg_end = (offset + len) >> PAGE_SHIFT;
> > -
> > - /* avoid gc operation during block exchange */
> > - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > -
> > down_write(&F2FS_I(inode)->i_mmap_sem);
> > /* write out all dirty pages from offset */
> > ret = filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
> > if (ret)
> > goto out_unlock;
> >
> > - truncate_pagecache(inode, offset);
> > -
> > - ret = f2fs_do_collapse(inode, pg_start, pg_end);
> > + ret = f2fs_do_collapse(inode, offset, len);
> > if (ret)
> > goto out_unlock;
> >
> > @@ -1242,7 +1240,6 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> > f2fs_i_size_write(inode, new_size);
> > out_unlock:
> > up_write(&F2FS_I(inode)->i_mmap_sem);
> > - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > return ret;
> > }
> >
> > @@ -1417,9 +1414,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >
> > f2fs_balance_fs(sbi, true);
> >
> > - /* avoid gc operation during block exchange */
> > - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > -
> > down_write(&F2FS_I(inode)->i_mmap_sem);
> > ret = f2fs_truncate_blocks(inode, i_size_read(inode), true);
> > if (ret)
> > @@ -1430,13 +1424,15 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> > if (ret)
> > goto out;
> >
> > - truncate_pagecache(inode, offset);
> > -
> > pg_start = offset >> PAGE_SHIFT;
> > pg_end = (offset + len) >> PAGE_SHIFT;
> > delta = pg_end - pg_start;
> > idx = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
> >
> > + /* avoid gc operation during block exchange */
> > + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > + truncate_pagecache(inode, offset);
> > +
> > while (!ret && idx > pg_start) {
> > nr = idx - pg_start;
> > if (nr > delta)
> > @@ -1450,6 +1446,7 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> > idx + delta, nr, false);
> > f2fs_unlock_op(sbi);
> > }
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >
> > /* write out all moved pages, if possible */
> > filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
> > @@ -1459,7 +1456,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> > f2fs_i_size_write(inode, new_size);
> > out:
> > up_write(&F2FS_I(inode)->i_mmap_sem);
> > - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > return ret;
> > }
> >
> > @@ -1706,8 +1702,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >
> > inode_lock(inode);
> >
> > - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > -
> > if (f2fs_is_atomic_file(inode)) {
> > if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
> > ret = -EINVAL;
> > @@ -1718,6 +1712,8 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> > if (ret)
> > goto out;
> >
> > + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > +
> > if (!get_dirty_pages(inode))
> > goto skip_flush;
> >
> > @@ -1725,18 +1721,20 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> > "Unexpected flush for atomic writes: ino=%lu, npages=%u",
> > inode->i_ino, get_dirty_pages(inode));
> > ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
> > - if (ret)
> > + if (ret) {
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > goto out;
> > + }
> > skip_flush:
> > set_inode_flag(inode, FI_ATOMIC_FILE);
> > clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> > - f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >
> > + f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> > F2FS_I(inode)->inmem_task = current;
> > stat_inc_atomic_write(inode);
> > stat_update_max_atomic_write(inode);
> > out:
> > - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > inode_unlock(inode);
> > mnt_drop_write_file(filp);
> > return ret;
> > @@ -1754,9 +1752,9 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> > if (ret)
> > return ret;
> >
> > - inode_lock(inode);
> > + f2fs_balance_fs(F2FS_I_SB(inode), true);
> >
> > - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > + inode_lock(inode);
> >
> > if (f2fs_is_volatile_file(inode)) {
> > ret = -EINVAL;
> > @@ -1782,7 +1780,6 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> > clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> > ret = -EINVAL;
> > }
> > - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > inode_unlock(inode);
> > mnt_drop_write_file(filp);
> > return ret;
> > @@ -2378,15 +2375,10 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> > }
> >
> > inode_lock(src);
> > - down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> > if (src != dst) {
> > ret = -EBUSY;
> > if (!inode_trylock(dst))
> > goto out;
> > - if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE])) {
> > - inode_unlock(dst);
> > - goto out;
> > - }
> > }
> >
> > ret = -EINVAL;
> > @@ -2431,6 +2423,14 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> > goto out_unlock;
> >
> > f2fs_balance_fs(sbi, true);
> > +
> > + down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> > + if (src != dst) {
> > + ret = -EBUSY;
> > + if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE]))
> > + goto out_src;
> > + }
> > +
> > f2fs_lock_op(sbi);
> > ret = __exchange_data_block(src, dst, pos_in >> F2FS_BLKSIZE_BITS,
> > pos_out >> F2FS_BLKSIZE_BITS,
> > @@ -2443,13 +2443,15 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> > f2fs_i_size_write(dst, dst_osize);
> > }
> > f2fs_unlock_op(sbi);
> > -out_unlock:
> > - if (src != dst) {
> > +
> > + if (src != dst)
> > up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
> > +out_src:
> > + up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> > +out_unlock:
> > + if (src != dst)
> > inode_unlock(dst);
> > - }
> > out:
> > - up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> > inode_unlock(src);
> > return ret;
> > }
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index e352fbd33848..cac317e37306 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -884,6 +884,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> > if (!down_write_trylock(
> > &F2FS_I(inode)->i_gc_rwsem[WRITE])) {
> > iput(inode);
> > + sbi->skipped_gc_rwsem++;
> > continue;
> > }
> >
> > @@ -913,6 +914,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> > continue;
> > if (!down_write_trylock(
> > &fi->i_gc_rwsem[WRITE])) {
> > + sbi->skipped_gc_rwsem++;
> > up_write(&fi->i_gc_rwsem[READ]);
> > continue;
> > }
> > @@ -1062,6 +1064,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> > prefree_segments(sbi));
> >
> > cpc.reason = __get_cp_reason(sbi);
> > + sbi->skipped_gc_rwsem = 0;
> > gc_more:
> > if (unlikely(!(sbi->sb->s_flags & SB_ACTIVE))) {
> > ret = -EINVAL;
> > @@ -1103,7 +1106,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> > total_freed += seg_freed;
> >
> > if (gc_type == FG_GC) {
> > - if (sbi->skipped_atomic_files[FG_GC] > last_skipped)
> > + if (sbi->skipped_atomic_files[FG_GC] > last_skipped ||
> > + sbi->skipped_gc_rwsem)
>
> There should be other foreground ops like DIO can race with GC, in such case, if
> we increase sbi->skipped_gc_rwsem, and call f2fs_drop_inmem_pages_all() to drop
> inmem pages later, it doesn't help?

Let me add a condition to decide that.

>
> > skipped_round++;
> > last_skipped = sbi->skipped_atomic_files[FG_GC];
> > round++;
> > @@ -1112,15 +1116,21 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> > if (gc_type == FG_GC)
> > sbi->cur_victim_sec = NULL_SEGNO;
> >
> > - if (!sync) {
> > - if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
> > - if (skipped_round > MAX_SKIP_ATOMIC_COUNT &&
> > - skipped_round * 2 >= round)
> > - f2fs_drop_inmem_pages_all(sbi, true);
> > + if (sync)
> > + goto stop;
> > +
> > + if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
> > + if (skipped_round <= MAX_SKIP_GC_COUNT ||
> > + skipped_round * 2 < round) {
> > segno = NULL_SEGNO;
> > goto gc_more;
> > }
> >
> > + if (sbi->skipped_atomic_files[FG_GC] == last_skipped) {
> > + f2fs_drop_inmem_pages_all(sbi, true);
> > + segno = NULL_SEGNO;
> > + goto gc_more;
> > + }
> > if (gc_type == FG_GC)
> > ret = f2fs_write_checkpoint(sbi, &cpc);
> > }
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 3662e1f429b4..15b3b095fd58 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -444,10 +444,12 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> > struct f2fs_inode_info *fi = F2FS_I(inode);
> > int err;
> >
> > - f2fs_balance_fs(sbi, true);
> > + f2fs_balance_fs(F2FS_I_SB(inode), true);
>
> We don't need to change sbi to F2FS_I_SB(inode).
>
> down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);

Done.

>
> Thanks,
>
> > +
> > f2fs_lock_op(sbi);
> >
> > set_inode_flag(inode, FI_ATOMIC_COMMIT);
> > + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >
> > mutex_lock(&fi->inmem_lock);
> > err = __f2fs_commit_inmem_pages(inode);
> > @@ -458,6 +460,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> > spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> > mutex_unlock(&fi->inmem_lock);
> >
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > clear_inode_flag(inode, FI_ATOMIC_COMMIT);
> >
> > f2fs_unlock_op(sbi);
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index 50495515f0a0..b3d9e317ff0c 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -215,7 +215,7 @@ struct segment_allocation {
> > #define IS_DUMMY_WRITTEN_PAGE(page) \
> > (page_private(page) == (unsigned long)DUMMY_WRITTEN_PAGE)
> >
> > -#define MAX_SKIP_ATOMIC_COUNT 16
> > +#define MAX_SKIP_GC_COUNT 16
> >
> > struct inmem_pages {
> > struct list_head list;
> >