linux-ext4 - Re: [PATCH] ext4: group cache is added in ext4_mb_discard

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Message-id: <56E2631B-9D71-4B96-9F2C-D469F6994598@sun.com>
Date:	Wed, 31 Mar 2010 09:03:56 -0600
From:	Andreas Dilger <adilger@....com>
To:	jing zhang <zj.barak@...il.com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] ext4: group cache is added in
 ext4_mb_discard_preallocations()

On 2010-03-30, at 06:36, jing zhang wrote:
> --- linux-2.6.32/fs/ext4/mballoc.c	2009-12-03 11:51:22.000000000 +0800
> +++ ext4_mm_leak/mballoc-13.c	2010-03-30 20:28:08.000000000 +0800
> @@ -4183,12 +4183,20 @@ static int ext4_mb_discard_preallocation
> 	trace_ext4_mb_discard_preallocations(sb, needed);
> -	for (i = 0; i < ngroups && needed > 0; i++) {
> -		ret = ext4_mb_discard_group_preallocations(sb, i, needed);
> +	if (needed <= 0)
> +		return freed;
> +	for (i = 0; i < ngroups; i++) {
> +		if (grp_cache >= ngroups)
> +			grp_cache -= ngroups;
> +		ret = ext4_mb_discard_group_preallocations(sb, grp_cache, needed);


Anything that is walking every group in the filesystem is going to hit  
problems on large filesystems.  This seems like something that needs  
to be fixed in a different way (e.g. keeping a list of preallocations).

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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