On 04/05, Chao Yu wrote:
> On 2023/4/5 5:39, Jaegeuk Kim wrote:
> > Can we do like this?
> >
> > From 9a58f0e59364241aa31b555cfe793d278e39b0dc Mon Sep 17 00:00:00 2001
> > From: Jaegeuk Kim <jaeg...@kernel.org>
> > Date: Tue, 4 Apr 2023 14:36:00 -0700
> > Subject: [PATCH] f2fs: do checkpoint when there's not enough free sections
> >
> > We didn't do checkpoint in FG_GC case, which may cause losing to reclaim
> > prefree
> > sctions in time.
> >
> > Fixes: 6f8d4455060d ("f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc")
> > Signed-off-by: Chao Yu <c...@kernel.org>
> > Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
> > ---
> > fs/f2fs/gc.c | 24 +++++++++++-------------
> > 1 file changed, 11 insertions(+), 13 deletions(-)
> >
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index 56c53dbe05c9..f1d0dd9c5a6c 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -1806,6 +1806,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct
> > f2fs_gc_control *gc_control)
> > };
> > unsigned int skipped_round = 0, round = 0;
> > unsigned int upper_secs;
> > + bool stop_gc = false;
> > trace_f2fs_gc_begin(sbi->sb, gc_type, gc_control->no_bg_gc,
> > gc_control->nr_free_secs,
> > @@ -1876,19 +1877,15 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct
> > f2fs_gc_control *gc_control)
> > (gc_type == FG_GC) ? sec_freed : 0, 0)) {
> > if (gc_type == FG_GC && sec_freed < gc_control->nr_free_secs)
> > goto go_gc_more;
> > - goto stop;
> > - }
> > -
> > - /* FG_GC stops GC by skip_count */
> > - if (gc_type == FG_GC) {
> > + stop_gc = true;
>
> I guess below condition is for emergency recycle of prefree segments during
> foreground GC, in order to avoid exhausting free sections due to to many
> metadata allocation during CP.
>
> if (free_sections(sbi) <= upper_secs + NR_GC_CHECKPOINT_SECS &&
> prefree_segments(sbi)) {
>
> But for common case, free_sections() is close to reserved_segments(), and
> upper_secs + NR_GC_CHECKPOINT_SECS value may be far smaller than
> free_sections(),
> so checkpoint may not be trggered as expected, IIUC.
>
> So it's fine to just trigger CP in the end of foreground garbage collection?
My major concern is to avoid unnecessary checkpointing given multiple FG_GC
requests were pending in parallel. And, I don't want to add so many combination
which gives so many corner cases, and feel f2fs_gc() needs to call checkpoint
automatically in the worst case scenario only.
By the way, do we just need to call checkpoint here including FG_GC as well?
1832
1833 if (gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) {
1834 /*
1835 * For example, if there are many prefree_segments below
given
1836 * threshold, we can make them free by checkpoint. Then, we
1837 * secure free segments which doesn't need fggc any more.
1838 */
1839 if (prefree_segments(sbi)) {
1840 ret = f2fs_write_checkpoint(sbi, &cpc);
1841 if (ret)
1842 goto stop;
1843 }
1844 if (has_not_enough_free_secs(sbi, 0, 0))
1845 gc_type = FG_GC;
1846 }
>
> One other concern is for those path as below:
> - disable_checkpoint
> - ioc_gc
> - ioc_gc_range
> - ioc_resize
> ...
I think the upper caller should decide to call checkpoint, if they want to
reclaim the prefree likewise f2fs_disable_checkpoint.
>
> We've passed gc_type as FG_GC, but the demand here is to migrate block in
> time,
> rather than dirtying blocks, and callers don't expect checkpoint in f2fs_gc(),
> instead the callers will do the checkpoit as it needs.
>
> That means it's better to decouple FG_GC and write_checkpoint behavior, so I
> added another parameter .reclaim_space to just let f2fs_balance_fs() to
> trigger
> checkpoit in the end of f2fs_gc().
>
> Thanks,
>
> > + } else if (gc_type == FG_GC) {
> > + /* FG_GC stops GC by skip_count */
> > if (sbi->skipped_gc_rwsem)
> > skipped_round++;
> > round++;
> > if (skipped_round > MAX_SKIP_GC_COUNT &&
> > - skipped_round * 2 >= round) {
> > - ret = f2fs_write_checkpoint(sbi, &cpc);
> > - goto stop;
> > - }
> > + skipped_round * 2 >= round)
> > + stop_gc = true;
> > }
> > __get_secs_required(sbi, NULL, &upper_secs, NULL);
> > @@ -1901,12 +1898,13 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct
> > f2fs_gc_control *gc_control)
> > prefree_segments(sbi)) {
> > ret = f2fs_write_checkpoint(sbi, &cpc);
> > if (ret)
> > - goto stop;
> > + stop_gc = true;
> > }
> > go_gc_more:
> > - segno = NULL_SEGNO;
> > - goto gc_more;
> > -
> > + if (!stop_gc) {
> > + segno = NULL_SEGNO;
> > + goto gc_more;
> > + }
> > stop:
> > SIT_I(sbi)->last_victim[ALLOC_NEXT] = 0;
> > SIT_I(sbi)->last_victim[FLUSH_DEVICE] = gc_control->victim_segno;
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