linux-ext4 - Re: [PATCH 2/5] ext4: speed up group trim with the right free block count.

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Message-ID: <20110711040658.GF28763@thunk.org>
Date:	Mon, 11 Jul 2011 00:06:58 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Tao Ma <tm@....ma>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/5] ext4: speed up group trim with the right free
 block count.

On Fri, Jul 01, 2011 at 11:27:53PM +0800, 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.
> 
> Reviewed-by: Andreas Dilger <adilger@...ger.ca>
> Signed-off-by: Tao Ma <boyu.mt@...bao.com>

Added to the ext4 tree, thanks.

					- Ted
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