[Devel] Re: [PATCH 2.6.19-rc3] VFS: per-sb dentry lru list

[Vasily Averin]

Hello Neil

Neil Brown wrote:
> On Wednesday November 1, vvs at sw.ru wrote:
>> Currently we have 3 type of functions that works with dentry_unused list:
>>
>> 1) prune_dcache(NULL) -- called from shrink_dcache_memory, frees the memory and
>> requires global LRU. works well in current implementation.
>> 2) prune_dcache(sb)  -- called from shrink_dcache_parent(), frees subtree, LRU
>> is not need here.  Current implementation uses global LRU for these purposes, it
>> is ineffective, and patch from Neil Brown fixes this issue.
>> 3) shrink_dcache_sb() -- called when we need to free the unused dentries for
>> given super block. Current implementation is not effective too, and per-sb LRU
>> would be the best solution here. On the other hand patch from Neil Brown is much
>> better than current implementation.
>>
>> In general I think that we should approve Neil Brown's patch. We (I and Kirill
>> Korotaev) are ready to acknowledge it when the following remarks fill be fixed:
> 
> 
>> - it seems for me list_splice() is not required inside
>>   prune_dcache(),
> 
> Yes, the list should be empty when we finish so you are right.
> 
>> - DCACHE_REFERENCED dentries should not be removed from private list to
>> dentry_unused list, this flag should be ignored if the private list is used,
> 
> Agreed.
> 
>> - count argument should be ignored in this case too, we want to free all the
>> dentries in private list,
> 
> Agreed.
> 
>> - when we shrink the whole super block we should free per-sb anonymous dentries
>> too (please see Kirill Korotaev's letter)
>>
> 
> Yes.  Unfortunately I don't think it is as easy as it sounds.
> I'll have a closer look.
> 
> 
>> Then I'm going to prepare new patch that will enhance the shrink_dcache_sb()
>> performance:
>> - we can add new list head into struct superblock and use it in
>> shrink_dcache_sb() instead of temporal private list. We will check is it empty
>> in dput() and add the new unused dentries to per-sb list instead of
>> dentry_unused list.
> 
> I think that makes sense.  It means that you end up doing less work in
> select_parent, because the work has already been done in dput.
> 
> How is the patch going?

Please see patches in attach files:
first one is incremental for your patch,
second one is merged version.

It would be very interesting to know your opinion about these changes.

thank you,
	Vasily Averin
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: diff-vfs-shrink-dcache-NBaddon-20061103
URL: <http://lists.openvz.org/pipermail/devel/attachments/20061114/1aed5784/attachment-0002.ksh>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: diff-vfs-shrink-dcache-20061103
URL: <http://lists.openvz.org/pipermail/devel/attachments/20061114/1aed5784/attachment-0003.ksh>