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Subject: Re: [PATCH] ocfs2: fix potential soft lockup during fstrim
To:     Gang He <ghe@suse.com>, mark@fasheh.com, jlbec@evilplan.org
Cc:     linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com,
        akpm@linux-foundation.org
References: <20200927015815.14904-1-ghe@suse.com>
From:   Joseph Qi <joseph.qi@linux.alibaba.com>
Message-ID: <cd133863-e81e-69f3-74da-bac4f52beb21@linux.alibaba.com>
Date:   Sun, 27 Sep 2020 10:59:38 +0800
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On 2020/9/27 09:58, Gang He wrote:
> When we discard unused blocks on a mounted ocfs2 filesystem, fstrim
> handles each block goup with locking/unlocking global bitmap meta-file
> repeatedly. we should let fstrim thread take a break(if need) between
> unlock and lock, this will avoid the potential soft lockup problem,
> and also gives the upper applications more IO opportunities, these
> applications are not blocked for too long at writing files.
> 
> Signed-off-by: Gang He <ghe@suse.com>

It makes sense.
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>

> ---
>  fs/ocfs2/alloc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> index 4c1b90442d6f..2cf9321919b5 100644
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -7654,8 +7654,10 @@ int ocfs2_trim_mainbm(struct super_block *sb, struct fstrim_range *range)
>  	 * main_bm related locks for avoiding the current IO starve, then go to
>  	 * trim the next group
>  	 */
> -	if (ret >= 0 && group <= last_group)
> +	if (ret >= 0 && group <= last_group) {
> +		cond_resched();
>  		goto next_group;
> +	}
>  out:
>  	range->len = trimmed * sb->s_blocksize;
>  	return ret;
>