Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 18 Feb 2020 15:27:14 -0800
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 3/3] f2fs: skip migration only when BG_GC is
 called
Message-ID: <20200218232714.GB10213@google.com>
References: <20200214185855.217360-1-jaegeuk@kernel.org>
 <20200214185855.217360-3-jaegeuk@kernel.org>
 <9c497f3e-3399-e4a6-f81c-6c4a1f35e5bb@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <9c497f3e-3399-e4a6-f81c-6c4a1f35e5bb@huawei.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 02/17, Chao Yu wrote:
> On 2020/2/15 2:58, Jaegeuk Kim wrote:
> > FG_GC needs to move entire section more quickly.
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> >  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 bbf4db3f6bb4..1676eebc8c8b 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -1203,7 +1203,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
> >  
> >  		if (get_valid_blocks(sbi, segno, false) == 0)
> >  			goto freed;
> > -		if (__is_large_section(sbi) &&
> > +		if (gc_type == BG_GC && __is_large_section(sbi) &&
> >  				migrated >= sbi->migration_granularity)
> 
> I knew migrating one large section is a more efficient way, but this can
> increase long-tail latency of f2fs_balance_fs() occasionally, especially in
> extreme fragmented space.

FG_GC requires to wait for whole section migration which shows the entire
latency.

> 
> Thanks,
> 
> >  			goto skip;
> >  		if (!PageUptodate(sum_page) || unlikely(f2fs_cp_error(sbi)))
> >