linux-kernel - Re: [PATCH] f2fs: discard small invalid blocks in current active segments

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Message-ID: <fd445a69-d860-2185-bfef-bf037a1f513e@huawei.com>
Date:   Mon, 28 Aug 2017 17:59:52 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Yunlong Song <yunlong.song@...wei.com>, <jaegeuk@...nel.org>,
        <chao@...nel.org>, <yunlong.song@...oud.com>
CC:     <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] f2fs: discard small invalid blocks in current active
 segments

On 2017/8/26 20:49, Yunlong Song wrote:
> 1. write file A with 5 blocks to current empty active segment
> 2. remove file A
> 3. write checkpoint
> 4. write file B with 507 blocks to the same active segment
> 
> If file B is alive all the time, the blocks used by file A will never be
> discarded. So current active segment should also be treated as a candidate
> for small discards.

I don't think that would be a big issue, since there will not be any freezing
log headers, once log header moves, later invalid blocks could be discarded.

Thanks,

> 
> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
> ---
>  fs/f2fs/segment.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 8375257..a2e7c8f 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1339,7 +1339,9 @@ static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc,
>  		return false;
>  
>  	if (!force) {
> -		if (!test_opt(sbi, DISCARD) || !se->valid_blocks ||
> +		if (!test_opt(sbi, DISCARD) ||
> +			(!se->valid_blocks &&
> +			!IS_CURSEG(sbi, cpc->trim_start)) ||
>  			SM_I(sbi)->dcc_info->nr_discards >=
>  				SM_I(sbi)->dcc_info->max_discards)
>  			return false;
>