linux-kernel - Re: [PATCH] f2fs: fix the discard thread sleep timeout under high utilization

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Date:   Mon, 15 Mar 2021 14:12:44 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Sahitya Tummala <stummala@...eaurora.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] f2fs: fix the discard thread sleep timeout under high
 utilization

Sahitya,

On 2021/3/15 12:56, Sahitya Tummala wrote:
> When f2fs is heavily utilized over 80%, the current discard policy
> sets the max sleep timeout of discard thread as 50ms
> (DEF_MIN_DISCARD_ISSUE_TIME). But this is set even when there are
> no pending discard commands to be issued. This results into
> unnecessary frequent and periodic wake ups of the discard thread.
> This patch adds check for pending  discard commands in addition
> to heavy utilization condition to prevent those wake ups.

Could this commit fix your issue?

https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev&id=43f8c47ea7d59c7b2270835f1d7c4618a1ea27b6

Thanks,

> 
> Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>
> ---
>   fs/f2fs/segment.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index dced46c..df30220 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1112,6 +1112,8 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
>   				struct discard_policy *dpolicy,
>   				int discard_type, unsigned int granularity)
>   {
> +	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> +
>   	/* common policy */
>   	dpolicy->type = discard_type;
>   	dpolicy->sync = true;
> @@ -1129,7 +1131,8 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
>   		dpolicy->io_aware = true;
>   		dpolicy->sync = false;
>   		dpolicy->ordered = true;
> -		if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
> +		if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL &&
> +				atomic_read(&dcc->discard_cmd_cnt)) {
>   			dpolicy->granularity = 1;
>   			dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;
>   		}
>