[Devel] Re: [PATCH 04/10] memcg: skip memcg kmem allocations in specified code regions

[Glauber Costa]

On 07/30/2012 04:50 PM, Kirill A. Shutemov wrote:
> On Wed, Jul 25, 2012 at 06:38:15PM +0400, Glauber Costa wrote:
>> This patch creates a mechanism that skip memcg allocations during
>> certain pieces of our core code. It basically works in the same way
>> as preempt_disable()/preempt_enable(): By marking a region under
>> which all allocations will be accounted to the root memcg.
>>
>> We need this to prevent races in early cache creation, when we
>> allocate data using caches that are not necessarily created already.
> 
> Why not a GFP_* flag?
> 

The main reason for this is to prevent nested calls of
kmem_cache_create(), since they could create (and in my tests, do
create) funny circular dependencies with each other. So the cache
creation itself would proceed without involving memcg.

At first, it is a bit weird to have cache creation itself depending on a
allocation flag test.