linux-ext4 - Re: [PATCH 1/4] ext4: use stream-alloc when mb_group

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Message-ID: <20111026091710.GS31921@thunk.org>
Date:	Wed, 26 Oct 2011 05:17:10 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Robin Dong <hao.bigrat@...il.com>
Cc:	linux-ext4@...r.kernel.org, Robin Dong <sanbai@...bao.com>
Subject: Re: [PATCH 1/4] ext4: use stream-alloc when mb_group_prealloc set
 to zero

On Thu, Sep 15, 2011 at 03:09:37PM +0800, Robin Dong wrote:
> From: Robin Dong <sanbai@...bao.com>
> 
> The kernel will crash on 
> 
> ext4_mb_mark_diskspace_used:
> 	BUG_ON(ac->ac_b_ex.fe_len <= 0);
> 
> after we set /sys/fs/ext4/sda/mb_group_prealloc to zero and create new files in an ext4 filesystem.
> 
> The reason is: ac_b_ex.fe_len also set to zero(mb_group_prealloc) in ext4_mb_normalize_group_request
> because the ac_flags contains EXT4_MB_HINT_GROUP_ALLOC.
> 
> I think when someone set mb_group_prealloc to zero, it means DO NOT USE GROUP PREALLOCATION,
> so we should set alloc-strategy to STREAM in this case.
> 
> Signed-off-by: Robin Dong <sanbai@...bao.com>

Thanks, applied.

						- Ted
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