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Date:   Thu, 9 Nov 2017 09:59:15 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Yunlong Song <yunlong.song@...wei.com>
Cc:     Chao Yu <yuchao0@...wei.com>, chao@...nel.org,
        yunlong.song@...oud.com, miaoxie@...wei.com,
        bintian.wang@...wei.com, linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: add bug_on when f2fs_gc even fails to get one
 victim

On 11/08, Yunlong Song wrote:
> So we should use f2fs_bug_on(sbi, !total_freed && !sync && gc_type ==
> FG_GC);

f2fs_bug_on(sbi, !total_freed && has_not_enough_free_secs(sbi, 0, 0)); ?

> 
> On 2017/11/7 14:56, Chao Yu wrote:
> > On 2017/11/7 12:01, Yunlong Song wrote:
> > > Sorry, misunderstanding, because I think when sync == true, FG_GC does not
> > > check has_not_enough_free_secs, so maybe it does not have to do any gc
> > > at all.
> > > For example, if there are 100 segments for f2fs, and 20 segments are full or
> > > valid blocks over fggc_threshold, then it is correct to fail in get victim.
> > > 
> > > 
> > > On 2017/11/7 11:26, Jaegeuk Kim wrote:
> > > > On 11/07, Yunlong Song wrote:
> > > > > Because I find that some out-of-free problem is caused by the failure
> > > > > of get victim target. For example, chao has pointed out that he has
> > > > > found out a bug when adding this bug_on last week.
> > > > That's NOT what I asked. Why not checking FG_GC all the time like this?
> > > > 
> > > > f2fs_bug_on(sbi, !total_freed && gc_type == FG_GC);
> > ioctl(F2FS_IOC_GARBAGE_COLLECT, &1) will simply trigger this bug_on, so we
> > have to check the conditon only when we run out-of-free-space?
> > 
> > Thanks,
> > 
> > > > > On 2017/11/7 10:40, Jaegeuk Kim wrote:
> > > > > > On 11/06, Jaegeuk Kim wrote:
> > > > > > > On 11/06, Yunlong Song wrote:
> > > > > > > > Agree.
> > > > > > > > 
> > > > > > > > On 2017/11/3 11:44, Jaegeuk Kim wrote:
> > > > > > > > > On 10/13, Yunlong Song wrote:
> > > > > > > > > > This can help us to debug on some corner case.
> > > > > > > > > > 
> > > > > > > > > > Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
> > > > > > > > > > Signed-off-by: Chao Yu <yuchao0@...wei.com>
> > > > > > > > > > ---
> > > > > > > > > >      fs/f2fs/gc.c | 6 +++++-
> > > > > > > > > >      1 file changed, 5 insertions(+), 1 deletion(-)
> > > > > > > > > > 
> > > > > > > > > > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > > > > > > > > > index 197ebf4..2b03202 100644
> > > > > > > > > > --- a/fs/f2fs/gc.c
> > > > > > > > > > +++ b/fs/f2fs/gc.c
> > > > > > > > > > @@ -986,6 +986,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> > > > > > > > > >      		.ilist = LIST_HEAD_INIT(gc_list.ilist),
> > > > > > > > > >      		.iroot = RADIX_TREE_INIT(GFP_NOFS),
> > > > > > > > > >      	};
> > > > > > > > > > +	bool need_fggc = false;
> > > > > > > > > >      	trace_f2fs_gc_begin(sbi->sb, sync, background,
> > > > > > > > > >      				get_pages(sbi, F2FS_DIRTY_NODES),
> > > > > > > > > > @@ -1018,8 +1019,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> > > > > > > > > >      			if (ret)
> > > > > > > > > >      				goto stop;
> > > > > > > > > >      		}
> > > > > > > > > > -		if (has_not_enough_free_secs(sbi, 0, 0))
> > > > > > > > > > +		if (has_not_enough_free_secs(sbi, 0, 0)) {
> > > > > > > > > >      			gc_type = FG_GC;
> > > > > > > > > > +			need_fggc = true;
> > > > > > > > > > +		}
> > > > > > > > > >      	}
> > > > > > > > > >      	/* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
> > > > > > > > > > @@ -1028,6 +1031,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> > > > > > > > > >      		goto stop;
> > > > > > > > > >      	}
> > > > > > > > > >      	if (!__get_victim(sbi, &segno, gc_type)) {
> > > > > > > > > > +		f2fs_bug_on(sbi, !total_freed && need_fggc);
> > > > > > > > > Just like this?
> > > > > > > > That's OK.
> > > > > > > I'm not quite sure whether this is really a bug_on case.
> > > > > > > Let me make it WARN_ON() for debugging purpose first.
> > > > > > BTW, why is this the special case where BG_GC detects FG_GC?
> > > > > > 
> > > > > > > Thanks,
> > > > > > > 
> > > > > > > > > 		f2fs_bug_on(sbi, !total_freed && !sync && gc_type == FG_GC);
> > > > > > > > > 
> > > > > > > > > >      		ret = -ENODATA;
> > > > > > > > > >      		goto stop;
> > > > > > > > > >      	}
> > > > > > > > > > -- 
> > > > > > > > > > 1.8.5.2
> > > > > > > > > .
> > > > > > > > > 
> > > > > > > > -- 
> > > > > > > > Thanks,
> > > > > > > > Yunlong Song
> > > > > > > > 
> > > > > > .
> > > > > > 
> > > > > -- 
> > > > > Thanks,
> > > > > Yunlong Song
> > > > > 
> > > > .
> > > > 
> > 
> > .
> > 
> 
> -- 
> Thanks,
> Yunlong Song
> 

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