Re: [PATCH v10 04/35] dentry: move to per-sb LRU locks

Glauber Costa
2013-06-06T08:03:22Z

On 06/06/2013 03:07 AM, Andrew Morton wrote:
> On Mon, 3 Jun 2013 23:29:33 +0400 Glauber Costa <glommer@openvz.org> wrote:
>
>> From: Dave Chinner <dchinner@redhat.com>
>>
>> With the dentry LRUs being per-sb structures, there is no real need
>> for a global dentry_lru_lock. The locking can be made more
>> fine-grained by moving to a per-sb LRU lock, isolating the LRU
>> operations of different filesytsems completely from each other.
>
> What's the point to this patch? Is it to enable some additional
> development, or is it a standalone performance tweak?
>
> If the latter then the patch obviously makes this dentry code bloatier
> and straight-line slower. So we're assuming that the multiprocessor
> contention-avoidance benefits will outweigh that cost. Got any proof
> of this?
>
>
This is preparation for the whole point of this series, which is to
abstract the lru manipulation into a list_lru. It is hard to do that
when the dcache has a single lock for all manipulations, and multiple
lists under its umbrella.

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