linux-ext4 - Re: [RFC] enable ext4 allocate blocks across group boundary

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Message-ID: <CAGBYx2aCtiy+ALRHMBh4sbUCBChWpwUH6wdBRVeZ1ENEJue6LA@mail.gmail.com>
Date:	Thu, 15 Mar 2012 12:15:22 +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 10:49 AM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> 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.
Here I meant they can be seen in buddy allocator.

Yongqiang.
>
>  I had a rough look at the code, current code does not handle the situation.
>
> Yongqiang.
>>
>> Cheers, Andreas
>>
>>
>>
>>
>>
>
>
>
> --
> Best Wishes
> Yongqiang Yang



-- 
Best Wishes
Yongqiang Yang
--
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