RE: [PATCH 5/5] f2fs: introduce a batched trim

[Chao Yu]

Hi Jaegeuk,

> -----Original Message-----
> From: linux-fsdevel-owner@xxxxxxxxxxxxxxx [mailto:linux-fsdevel-owner@xxxxxxxxxxxxxxx] On
> Behalf Of Jaegeuk Kim
> Sent: Wednesday, January 28, 2015 7:32 AM
> To: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Jaegeuk Kim
> Subject: [PATCH 5/5] f2fs: introduce a batched trim
> 
> This patch introduces a batched trimming feature, which submits split discard
> commands.

I didn't get it, why we should split discard commands. :(

Does smaller discarding for flash shows better performance or effect or safety?
Can you please explain more about this patch?

Thanks,

> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
>  fs/f2fs/f2fs.h    |  1 +
>  fs/f2fs/segment.c | 15 ++++++++++-----
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index c0b83d6..ec4d16b 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -104,6 +104,7 @@ enum {
>  	CP_DISCARD,
>  };
> 
> +#define BATCHED_TRIM_SEGMENTS	10
>  struct cp_control {
>  	int reason;
>  	__u64 trim_start;
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 31c4e57..6c9c784 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1066,14 +1066,19 @@ 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 + 1) {
> +		cpc.trim_start = start_segno;
> +		cpc.trim_end = min_t(unsigned int,
> +				start_segno + BATCHED_TRIM_SEGMENTS, 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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