Re: [f2fs-dev] [PATCH 3/6] f2fs: remove batched discard in f2fs_trim_fs

From: Jaegeuk Kim
Date: Wed Feb 22 2017 - 17:06:39 EST

On 02/22, Chao Yu wrote:
> On 2017/1/13 6:44, Jaegeuk Kim wrote:
> > We don't need to do multiple checkpoints, since we don't actually wait for
> > completion of discard commands during checkpoint.
> > Instead, we still need to avoid very big discard commands, since that large
> > discard can interfere block allocation.
>
> I hope we can keep this functionality and related sysfs interface, the main
> concern is that: for 16T size fragmented partition, at most there will be
> ~sizeof(u32)/2 4K blocks which could be invalid and needed to be discarded.
> After removal of in-batch discard, we have to handle billions of discard message
> with gc_mutex & cp_rwsem held, which will freeze f2fs for very long time.

The baseline of this patch is that we have a kernel thread to issue discard
commands asynchronously. So, I don't expect such the huge latency anymore.

Thanks,

>
> So I suggest we just set trim_sections to 512 segments (covers one GB) by
> default. How do you think?
>
> Thanks,
>
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > ---
> > Documentation/ABI/testing/sysfs-fs-f2fs | 6 ------
> > fs/f2fs/f2fs.h | 9 +-------
> > fs/f2fs/segment.c | 38 +++++++++++----------------------
> > fs/f2fs/super.c | 2 --
> > 4 files changed, 14 insertions(+), 41 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> > index a809f6005f14..df6b3f6e164a 100644
> > --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> > +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> > @@ -75,12 +75,6 @@ Contact: "Jaegeuk Kim" <jaegeuk.kim@xxxxxxxxxxx>
> > Description:
> > Controls the memory footprint used by f2fs.
> >
> > -What: /sys/fs/f2fs/<disk>/trim_sections
> > -Date: February 2015
> > -Contact: "Jaegeuk Kim" <jaegeuk@xxxxxxxxxx>
> > -Description:
> > - Controls the trimming rate in batch mode.
> > -
> > What: /sys/fs/f2fs/<disk>/cp_interval
> > Date: October 2015
> > Contact: "Jaegeuk Kim" <jaegeuk@xxxxxxxxxx>
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 548e75d18ec1..a2850bf2a487 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -128,11 +128,7 @@ enum {
> > CP_DISCARD,
> > };
> >
> > -#define DEF_BATCHED_TRIM_SECTIONS 2
> > -#define BATCHED_TRIM_SEGMENTS(sbi) \
> > - (SM_I(sbi)->trim_sections * (sbi)->segs_per_sec)
> > -#define BATCHED_TRIM_BLOCKS(sbi) \
> > - (BATCHED_TRIM_SEGMENTS(sbi) << (sbi)->log_blocks_per_seg)
> > +#define MAX_DISCARD_BLOCKS(sbi) (1 << (sbi)->log_blocks_per_seg)
> > #define DEF_CP_INTERVAL 60 /* 60 secs */
> > #define DEF_IDLE_INTERVAL 5 /* 5 secs */
> >
> > @@ -638,9 +634,6 @@ struct f2fs_sm_info {
> > int nr_discards; /* # of discards in the list */
> > int max_discards; /* max. discards to be issued */
> >
> > - /* for batched trimming */
> > - unsigned int trim_sections; /* # of sections to trim */
> > -
> > struct list_head sit_entry_set; /* sit entry set list */
> >
> > unsigned int ipu_policy; /* in-place-update policy */
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 73282108fa33..e6f3c6db7616 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -823,7 +823,8 @@ static void __add_discard_entry(struct f2fs_sb_info *sbi,
> > if (!list_empty(head)) {
> > last = list_last_entry(head, struct discard_entry, list);
> > if (START_BLOCK(sbi, cpc->trim_start) + start ==
> > - last->blkaddr + last->len) {
> > + last->blkaddr + last->len &&
> > + last->len <= MAX_DISCARD_BLOCKS(sbi)) {
> > last->len += end - start;
> > goto done;
> > }
> > @@ -1513,36 +1514,25 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
> > "Found FS corruption, run fsck to fix.");
> > goto out;
> > }
> > + if (sbi->discard_blks == 0)
> > + goto out;
> >
> > /* start/end segment number in main_area */
> > start_segno = (start <= MAIN_BLKADDR(sbi)) ? 0 : GET_SEGNO(sbi, start);
> > end_segno = (end >= MAX_BLKADDR(sbi)) ? MAIN_SEGS(sbi) - 1 :
> > GET_SEGNO(sbi, end);
> > + /*
> > + * do checkpoint to issue discard commands safely since we now can
> > + * use async discard.
> > + */
> > cpc.reason = CP_DISCARD;
> > cpc.trim_minlen = max_t(__u64, 1, F2FS_BYTES_TO_BLK(range->minlen));
> > + cpc.trim_start = start_segno;
> > + cpc.trim_end = end_segno;
> >
> > - /* do checkpoint to issue discard commands safely */
> > - for (; start_segno <= end_segno; start_segno = cpc.trim_end + 1) {
> > - cpc.trim_start = start_segno;
> > -
> > - if (sbi->discard_blks == 0)
> > - break;
> > - else if (sbi->discard_blks < BATCHED_TRIM_BLOCKS(sbi))
> > - cpc.trim_end = end_segno;
> > - else
> > - cpc.trim_end = min_t(unsigned int,
> > - rounddown(start_segno +
> > - BATCHED_TRIM_SEGMENTS(sbi),
> > - sbi->segs_per_sec) - 1, end_segno);
> > -
> > - mutex_lock(&sbi->gc_mutex);
> > - err = write_checkpoint(sbi, &cpc);
> > - mutex_unlock(&sbi->gc_mutex);
> > - if (err)
> > - break;
> > -
> > - schedule();
> > - }
> > + mutex_lock(&sbi->gc_mutex);
> > + err = write_checkpoint(sbi, &cpc);
> > + mutex_unlock(&sbi->gc_mutex);
> > out:
> > range->len = F2FS_BLK_TO_BYTES(cpc.trimmed);
> > return err;
> > @@ -2708,8 +2698,6 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
> > sm_info->nr_discards = 0;
> > sm_info->max_discards = 0;
> >
> > - sm_info->trim_sections = DEF_BATCHED_TRIM_SECTIONS;
> > -
> > INIT_LIST_HEAD(&sm_info->sit_entry_set);
> >
> > if (test_opt(sbi, FLUSH_MERGE) && !f2fs_readonly(sbi->sb)) {
> > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> > index 461c29043aec..37d40d8aa9c4 100644
> > --- a/fs/f2fs/super.c
> > +++ b/fs/f2fs/super.c
> > @@ -284,7 +284,6 @@ F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_no_gc_sleep_time, no_gc_sleep_time);
> > F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_idle, gc_idle);
> > F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, reclaim_segments, rec_prefree_segments);
> > F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, max_small_discards, max_discards);
> > -F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, batched_trim_sections, trim_sections);
> > F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, ipu_policy, ipu_policy);
> > F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_ipu_util, min_ipu_util);
> > F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_fsync_blocks, min_fsync_blocks);
> > @@ -309,7 +308,6 @@ static struct attribute *f2fs_attrs[] = {
> > ATTR_LIST(gc_idle),
> > ATTR_LIST(reclaim_segments),
> > ATTR_LIST(max_small_discards),
> > - ATTR_LIST(batched_trim_sections),
> > ATTR_LIST(ipu_policy),
> > ATTR_LIST(min_ipu_util),
> > ATTR_LIST(min_fsync_blocks),
> >
>
>
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