linux-kernel - Re: [PATCH 2/3] f2fs: schedule in between two continous batch discards

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Date:   Tue, 23 Aug 2016 09:53:53 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH 2/3] f2fs: schedule in between two continous batch
 discards

Hi Chao,

On Sun, Aug 21, 2016 at 11:21:30PM +0800, Chao Yu wrote:
> From: Chao Yu <yuchao0@...wei.com>
> 
> In batch discard approach of fstrim will grab/release gc_mutex lock
> repeatly, it makes contention of the lock becoming more intensive.
> 
> So after one batch discards were issued in checkpoint and the lock
> was released, it's better to do schedule() to increase opportunity
> of grabbing gc_mutex lock for other competitors.
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/segment.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 020767c..d0f74eb 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1305,6 +1305,8 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
>  		mutex_unlock(&sbi->gc_mutex);
>  		if (err)
>  			break;
> +
> +		schedule();

Hmm, if other thread is already waiting for gc_mutex, we don't need this here.
In order to avoid long latency, wouldn't it be enough to reduce the batch size?

Thanks,

>  	}
>  out:
>  	range->len = F2FS_BLK_TO_BYTES(cpc.trimmed);
> -- 
> 2.7.2