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Date:   Wed, 4 Apr 2018 20:51:15 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: enlarge block plug coverage

On 04/04, Chao Yu wrote:
> This patch enlarges block plug coverage in __issue_discard_cmd, in
> order to collect more pending bios before issuing them, to avoid
> being disturbed by previous discard I/O in IO aware discard mode.

Hmm, then we need to wait for huge discard IO for over 10 secs, which
will affect following read/write IOs accordingly. In order to avoid that,
we actually need to limit the discard size.

Thanks,

> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/segment.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 8f0b5ba46315..4287e208c040 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1208,10 +1208,12 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  		pend_list = &dcc->pend_list[i];
>  
>  		mutex_lock(&dcc->cmd_lock);
> +
> +		blk_start_plug(&plug);
> +
>  		if (list_empty(pend_list))
>  			goto next;
>  		f2fs_bug_on(sbi, !__check_rb_tree_consistence(sbi, &dcc->root));
> -		blk_start_plug(&plug);
>  		list_for_each_entry_safe(dc, tmp, pend_list, list) {
>  			f2fs_bug_on(sbi, dc->state != D_PREP);
>  
> @@ -1227,8 +1229,9 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  			if (++iter >= dpolicy->max_requests)
>  				break;
>  		}
> -		blk_finish_plug(&plug);
>  next:
> +		blk_finish_plug(&plug);
> +
>  		mutex_unlock(&dcc->cmd_lock);
>  
>  		if (iter >= dpolicy->max_requests)
> -- 
> 2.15.0.55.gc2ece9dc4de6

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