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Subject: Re: [f2fs-dev] [PATCH 3/3] f2fs: skip migration only when BG_GC is
 called
To:     Jaegeuk Kim <jaegeuk@kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
References: <20200214185855.217360-1-jaegeuk@kernel.org>
 <20200214185855.217360-3-jaegeuk@kernel.org>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <9c497f3e-3399-e4a6-f81c-6c4a1f35e5bb@huawei.com>
Date:   Mon, 17 Feb 2020 10:22:22 +0800
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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.

Thanks,

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