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Date:	Thu, 15 Mar 2012 10:49:19 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [RFC] enable ext4 allocate blocks across group boundary

On Thu, Mar 15, 2012 at 10:34 AM, Andreas Dilger <adilger@...ger.ca> wrote:
> On 2012-03-14, at 6:52 PM, Yongqiang Yang wrote:
>> Here is a proposal to enable ext4 allocate blocks across group boundary.
>>
>> Now ext4 allocates blocks within a single block group by locking a
>> group.   Flex_bg puts metadata blocks together, as a result,it
>> enlarges contiguous blocks.  So we can enable ext4 allocate blocks
>> within a flex block group. Inode allocation takes group lock as block
>> allocation,  I am not sure if we should allocate inode within single
>> group as before.
>>
>> If we do this, then the new group boundary will be flex block group
>> boundary.  I am not sure if it is worth doing.
>
> The maximum extent size is the same as a single block group, so there
> is relatively little value in doing this, IMHO.
nope.  The value comes from 2 aspects: 1. the preallocation can
preallocate much more space , 2. if  tail blocks of a group and head
blocks of the next group is free, then they can be treated as
contiguous blocks.

  I had a rough look at the code, current code does not handle the situation.

Yongqiang.
>
> Cheers, Andreas
>
>
>
>
>



-- 
Best Wishes
Yongqiang Yang
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