linux-kernel - Re: [f2fs-dev] [PATCH 5/5 v2] f2fs: introduce a batched trim

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Date:	Tue, 03 Feb 2015 11:48:22 +0900
From:	Changman Lee <cm224.lee@...sung.com>
To:	Jaegeuk Kim <jaegeuk@...nel.org>
Cc:	Chao Yu <chao2.yu@...sung.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 5/5 v2] f2fs: introduce a batched trim

Hi Jaegeuk,

IMHO, it looks better user could decide the size of trim considering latency of trim.
Otherwise, additional checkpoints user doesn't want will occur.

Regards,
Changman

On Mon, Feb 02, 2015 at 03:29:25PM -0800, Jaegeuk Kim wrote:
> Change long from v1:
>  o add description
>  o change the # of batched segments suggested by Chao
>  o make consistent for # of batched segments
> 
> This patch introduces a batched trimming feature, which submits split discard
> commands.
> 
> This patch introduces a batched trimming feature, which submits split discard
> commands.
> 
> This is to avoid long latency due to huge trim commands.
> If fstrim was triggered ranging from 0 to the end of device, we should lock
> all the checkpoint-related mutexes, resulting in very long latency.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/f2fs.h    |  2 ++
>  fs/f2fs/segment.c | 16 +++++++++++-----
>  2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 8231a59..ec5e66f 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -105,6 +105,8 @@ enum {
>  	CP_DISCARD,
>  };
>  
> +#define BATCHED_TRIM_SEGMENTS(sbi)	(((sbi)->segs_per_sec) << 5)
> +
>  struct cp_control {
>  	int reason;
>  	__u64 trim_start;
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 5ea57ec..b85bb97 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1066,14 +1066,20 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
>  	end_segno = (end >= MAX_BLKADDR(sbi)) ? MAIN_SEGS(sbi) - 1 :
>  						GET_SEGNO(sbi, end);
>  	cpc.reason = CP_DISCARD;
> -	cpc.trim_start = start_segno;
> -	cpc.trim_end = end_segno;
>  	cpc.trim_minlen = range->minlen >> sbi->log_blocksize;
>  
>  	/* do checkpoint to issue discard commands safely */
> -	mutex_lock(&sbi->gc_mutex);
> -	write_checkpoint(sbi, &cpc);
> -	mutex_unlock(&sbi->gc_mutex);
> +	for (; start_segno <= end_segno;
> +				start_segno += BATCHED_TRIM_SEGMENTS(sbi)) {
> +		cpc.trim_start = start_segno;
> +		cpc.trim_end = min_t(unsigned int,
> +				start_segno + BATCHED_TRIM_SEGMENTS (sbi) - 1,
> +				end_segno);
> +
> +		mutex_lock(&sbi->gc_mutex);
> +		write_checkpoint(sbi, &cpc);
> +		mutex_unlock(&sbi->gc_mutex);
> +	}
>  out:
>  	range->len = cpc.trimmed << sbi->log_blocksize;
>  	return 0;
> -- 
> 2.1.1
> 
> 
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