Re: [f2fs-dev] [PATCH 2/3] f2fs: run GCs synchronously given user requests

[Chao Yu]

On 2022/6/23 0:58, Jaegeuk Kim wrote:
> On 06/22, Chao Yu wrote:
> > On 2022/6/20 6:34, Jaegeuk Kim wrote:
> > > On 06/19, Chao Yu wrote:
> > > > On 2022/6/18 6:31, Jaegeuk Kim wrote:
> > > > > When users set GC_URGENT or GC_MID, they expected to do GCs right away.
> > > > > But, there's a condition to bypass it. Let's indicate we need to do now
> > > > > in the thread.
> > > >
> > > > .should_migrate_blocks is used to force migrating blocks in full
> > > > section, so what is the condition here? GC should not never select
> > > > a full section, right?
> > >
> > > I think it'll move a full section given .victim_segno is not NULL_SEGNO,
> > > as __get_victim will give a dirty segment all the time. wdyt?
> >
> > However, in gc_thread_fun() victim_segno is NULL_SEGNO all the time.
>
> What do you mean? The gc_thread thread sets NULL_SEGNO, which prevents
> from selecting the full section. But, f2fs_ioc_flush_device will set the
> segno to move, and f2fs_resize_fs calls do_garbage_collect directly.

Yes, but I didn't get why this patch updates .should_migrate_blocks for
gc_thread_func() case? If this is added to avoid breaking from below condition,
I guess it's not necessary, since victim selected from gc_thread_func() will
always be dirty, so get_valid_blocks(sbi, segno, true) == BLKS_PER_SEC(sbi)
will be false anyway? or am I missing something?

		/*
		 * stop BG_GC if there is not enough free sections.
		 * Or, stop GC if the segment becomes fully valid caused by
		 * race condition along with SSR block allocation.
		 */
		if ((gc_type == BG_GC && has_not_enough_free_secs(sbi, 0, 0)) ||
			(!force_migrate && get_valid_blocks(sbi, segno, true) ==
							BLKS_PER_SEC(sbi)))
			return submitted;

Thanks,

> > I guess .should_migrate_blocks should only be set to true for
> > F2FS_IOC_FLUSH_DEVICE/F2FS_IOC_RESIZE_FS case? rather than GC_URGENT or GC_MID
> > case? See commit 7dede88659df ("f2fs: fix to allow migrating fully valid segment").
> >
> > Thanks,
> >
> > > > Thanks,
> > > >
> > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > > > > ---
> > > > >     fs/f2fs/gc.c | 8 ++++++--
> > > > >     1 file changed, 6 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > > > > index d5fb426e0747..f4aa3c88118b 100644
> > > > > --- a/fs/f2fs/gc.c
> > > > > +++ b/fs/f2fs/gc.c
> > > > > @@ -37,7 +37,6 @@ static int gc_thread_func(void *data)
> > > > >     	unsigned int wait_ms;
> > > > >     	struct f2fs_gc_control gc_control = {
> > > > >     		.victim_segno = NULL_SEGNO,
> > > > > -		.should_migrate_blocks = false,
> > > > >     		.err_gc_skipped = false };
> > > > >     	wait_ms = gc_th->min_sleep_time;
> > > > > @@ -113,7 +112,10 @@ static int gc_thread_func(void *data)
> > > > >     				sbi->gc_mode == GC_URGENT_MID) {
> > > > >     			wait_ms = gc_th->urgent_sleep_time;
> > > > >     			f2fs_down_write(&sbi->gc_lock);
> > > > > +			gc_control.should_migrate_blocks = true;
> > > > >     			goto do_gc;
> > > > > +		} else {
> > > > > +			gc_control.should_migrate_blocks = false;
> > > > >     		}
> > > > >     		if (foreground) {
> > > > > @@ -139,7 +141,9 @@ static int gc_thread_func(void *data)
> > > > >     		if (!foreground)
> > > > >     			stat_inc_bggc_count(sbi->stat_info);
> > > > > -		sync_mode = F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_SYNC;
> > > > > +		sync_mode = F2FS_OPTION(sbi).bggc_mode == BGGC_MODE_SYNC ||
> > > > > +				sbi->gc_mode == GC_URGENT_HIGH ||
> > > > > +				sbi->gc_mode == GC_URGENT_MID;
> > > > >     		/* foreground GC was been triggered via f2fs_balance_fs() */
> > > > >     		if (foreground)