linux-ext4 - Re: [PATCH 2/4] ext4: speed up group trim with the right free block count.

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Message-Id: <D505F0D6-9049-4079-A350-DCCCC97A6338@dilger.ca>
Date:	Thu, 30 Jun 2011 10:35:57 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Tao Ma <tm@....ma>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 2/4] ext4: speed up group trim with the right free block count.

On 2011-06-30, at 8:50 AM, Tao Ma wrote:
> From: Tao Ma <boyu.mt@...bao.com>
> 
> When we trim some free blocks in a group of ext4, 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
> isn't appropriate.
> 
> 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.
> 
> Signed-off-by: Tao Ma <boyu.mt@...bao.com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> ---
> fs/ext4/mballoc.c |    5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 2336424..83fb04b 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4823,7 +4823,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 		   ext4_grpblk_t minblocks)
> {
> 	void *bitmap;
> -	ext4_grpblk_t next, count = 0;
> +	ext4_grpblk_t next, count = 0, free_count = 0;
> 	struct ext4_buddy e4b;
> 	int ret;
> 
> @@ -4850,6 +4850,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 					 next - start, group, &e4b);
> 			count += next - start;
> 		}
> +		free_count += next - start;
> 		start = next + 1;
> 
> 		if (fatal_signal_pending(current)) {
> @@ -4863,7 +4864,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 			ext4_lock_group(sb, group);
> 		}
> 
> -		if ((e4b.bd_info->bb_free - count) < minblocks)
> +		if ((e4b.bd_info->bb_free - free_count) < minblocks)
> 			break;
> 	}
> 	ext4_unlock_group(sb, group);
> -- 
> 1.7.4
> 
> --
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Cheers, Andreas





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