[Ocfs2-devel] Why ocfs2 haven't implemented "steal" for local_alloc system files?

[Younger Liu <younger.liu@huawei.com>]

On 2013/8/2 2:57, Srinivas Eeda wrote:
> On 08/01/2013 01:38 AM, Younger Liu wrote:
>> On 2013/8/1 15:20, Joel Becker wrote:
>>> Basically, there's so little in the cache that stealing would be too
>>> complex.  Really we just want to fall back to the global, and if that is
>>> empty, you're near enough ENOSPC that it doesn't much matter.
>>>
>>> Joel
>>>
>> Localalloc is a mount option. When mounting an ocfs2 volume, localalloc can
>> be set a larger size. For example, 2G or a larger number.
>>
>> In a multi-nodes cluster, all nodes mount ocfs2 volume with localalloc=2048
> Is there a proof that localalloc=2048 performs better than default 256Mb 
> ? local alloc currently looks for contiguous chunks. setting it to 2gb 
> means it has to scan the whole bitmap to find that big of a chunk which 
> in itself defeats the purpose of setting it to 2gb. I mean it might work 
> well for a filesystem that just got formatted but as it gets used 
> finding 2gb chunks is hard.

yes, I have proved that localalloc=2048 performs better, it improves about 5%.
In the scenario, ocfs2 volume stores virtual images which are very large, 
for example, 20G or 50G.

> 
>> for performance consideration, if a node claims space for a file, but there
>> is no space in the local_alloc and global_bitmap. It would return ENOSPC.
>> However, other nodes may have lots of space which have been claimed
>> in local_alloc, so ENOSPC cannot reflect the actual situation.
>>
>> IMO, if there is no space both in the local_alloc and global_bitmap,
>> it should steal space from other nodes local_alloc.
>>
>> Thx,
>> Younger.
>>
>>> On Wed, Jul 31, 2013 at 08:33:48PM -0700, Sunil Mushran wrote:
>>>> Because it makes no sense. Unlike inode/extent allocs, local_alloc is a
>>>> temporary cache. If you fail to allocate, you fallback to the global bitmap.
>>>>
>>>>
>>>> On Sat, Jul 27, 2013 at 3:27 AM, Younger Liu <younger.liu@huawei.com> wrote:
>>>>
>>>>> Hi,
>>>>>    While analyzing ocfs2 block allocation, I found:
>>>>>    When claiming space from inode_alloc (or extent_alloc) system files,
>>>>> if there is no enough space in inode_alloc (or extent_alloc) and
>>>>> global_bitmap, it could steal space from other slots.
>>>>>    But when claiming space from local_alloc system files, and no
>>>>> enough space in local_alloc and global_bitmap, it returns -ENOSPC.
>>>>>
>>>>>    Why ocfs2 haven't implemented "steal" for local_alloc system files?
>>>>>    Is there any some reasons?
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>> Ocfs2-devel at oss.oracle.com
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>>>>>
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>>
>>
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