linux-kernel - Re: [f2fs-dev] [PATCH 1/2] f2fs: do not select same victim right again

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Message-ID: <20190916153736.GA2493@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Mon, 16 Sep 2019 08:37:36 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: do not select same victim right
 again

On 09/16, Chao Yu wrote:
> On 2019/9/9 20:04, Jaegeuk Kim wrote:
> > On 09/09, Chao Yu wrote:
> >> On 2019/9/9 16:06, Jaegeuk Kim wrote:
> >>> On 09/09, Chao Yu wrote:
> >>>> On 2019/9/9 9:25, Jaegeuk Kim wrote:
> >>>>> GC must avoid select the same victim again.
> >>>>
> >>>> Blocks in previous victim will occupy addition free segment, I doubt after this
> >>>> change, FGGC may encounter out-of-free space issue more frequently.
> >>>
> >>> Hmm, actually this change seems wrong by sec_usage_check().
> >>> We may be able to avoid this only in the suspicious loop?
> >>>
> >>> ---
> >>>  fs/f2fs/gc.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>> index e88f98ddf396..5877bd729689 100644
> >>> --- a/fs/f2fs/gc.c
> >>> +++ b/fs/f2fs/gc.c
> >>> @@ -1326,7 +1326,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> >>>  		round++;
> >>>  	}
> >>>  
> >>> -	if (gc_type == FG_GC)
> >>> +	if (gc_type == FG_GC && seg_freed)
> >>
> >> That's original solution Sahitya provided to avoid infinite loop of GC, but I
> >> suggest to find the root cause first, then we added .invalid_segmap for that
> >> purpose.
> > 
> > I've checked the Sahitya's patch. So, it seems the problem can happen due to
> > is_alive or atomic_file.
> 
> For some conditions, this doesn't help, for example, two sections contain the
> same fewest valid blocks, it will cause to loop selecting them if it fails to
> migrate blocks.
> 
> How about keeping it as it is to find potential bug.

I think it'd be fine to merge this. Could you check the above scenario in more
detail?

Thanks,

> 
> Thanks,
> 
> > 
> >>
> >> Thanks,
> >>
> >>>  		sbi->cur_victim_sec = NULL_SEGNO;
> >>>  
> >>>  	if (sync)
> >>>
> > .
> >