linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: issue discard commands proactively in high fs utilization

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Date:   Tue, 14 May 2019 14:39:41 +0900
From:   Ju Hyung Park <qkrwngud825@...il.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: issue discard commands proactively in
 high fs utilization

On Wed, May 30, 2018 at 5:51 AM Jaegeuk Kim <jaegeuk@...nel.org> wrote:
>
> In the high utilization like over 80%, we don't expect huge # of large discard
> commands, but do many small pending discards which affects FTL GCs a lot.
> Let's issue them in that case.
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 6e40e536dae0..8c1f7a6bf178 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -915,6 +915,38 @@ static void __check_sit_bitmap(struct f2fs_sb_info *sbi,
> +                       dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;

Isn't this way too aggressive?

Discard thread will wake up on 50ms interval just because the user has
used 80% of space.
60,000ms vs 50ms is too much of a stark difference.

I feel something like 10 seconds(10,000ms) could be a much more
reasonable choice than this.

Thanks.