Re: [PATCH v2] ext3: speed up group trim with the right free block count.

[Jan Kara <jack@suse.cz>]

On Fri 21-01-11 22:19:36, Tao Ma wrote:
> On 01/21/2011 06:44 PM, Lukas Czerner wrote:
> > Nice catch, do you plan to do the same for ext4 ? Btw, I do not think
> > there is a need for new variable (free_count), you can as well do :
> >
> > free_blocks -= next - start;
> > ...
> > if (free_blocks < minblocks)
> > 	break;
> yeah, the extra varaible isn't needed. Here is the updated patch.
> 
> Regards,
> Tao
> 
> Subject: [PATCH v2] ext3: speed up group trim with the right free block count.
> From 48ab7651409df9b21dfaa9cec6a8db62467b8ca7 Mon Sep 17 00:00:00 2001
> From: Tao Ma <boyu.mt@taobao.com>
> Date: Fri, 21 Jan 2011 22:09:20 +0800
> Subject: [PATCH v2] ext3: speed up group trim with the right free block count.
> 
> When we trim some free blocks in a group of ext3, we should
> calculate the free blocks properly and check whether there are
> enough freed blocks left for us to trim. Current solution will
> only calculate free spaces if they are large for a trim which
> is wrong.
> 
> Let us see a small example:
> a group has 1.5M free which are 300k, 300k, 300k, 300k, 300k.
> And minblocks is 1M. With current solution, we have to iterate
> the whole group since these 300k will never be subtracted from
> 1.5M. But actually we should exit after we find the first 2
> free spaces since the left 3 chunks only sum up to 900K if we
> subtract the first 600K although they can't be trimed.
  Thanks. Merged.

							Honza
> 
> Cc: Jan Kara <jack@suse.cz>
> Cc: Lukas Czerner <lczerner@redhat.com>
> Signed-off-by: Tao Ma <boyu.mt@taobao.com>
> ---
>  fs/ext3/balloc.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ext3/balloc.c b/fs/ext3/balloc.c
> index 045995c..b9697f7 100644
> --- a/fs/ext3/balloc.c
> +++ b/fs/ext3/balloc.c
> @@ -1991,6 +1991,7 @@ ext3_grpblk_t ext3_trim_all_free(struct super_block *sb, unsigned int group,
>  		spin_unlock(sb_bgl_lock(sbi, group));
>  		percpu_counter_sub(&sbi->s_freeblocks_counter, next - start);
>  
> +		free_blocks -= next - start;
>  		/* Do not issue a TRIM on extents smaller than minblocks */
>  		if ((next - start) < minblocks)
>  			goto free_extent;
> @@ -2040,7 +2041,7 @@ free_extent:
>  		cond_resched();
>  
>  		/* No more suitable extents */
> -		if ((free_blocks - count) < minblocks)
> +		if (free_blocks < minblocks)
>  			break;
>  	}
>  
> -- 
> 1.7.1
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR