Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache control

Avi Kivity
2010-06-15T07:11:42Z

On 06/14/2010 08:40 PM, Balbir Singh wrote:
> * Avi Kivity<avi@redhat.com> [2010-06-14 18:34:58]:
>
>
>> On 06/14/2010 06:12 PM, Dave Hansen wrote:
>>
>>> On Mon, 2010-06-14 at 14:18 +0530, Balbir Singh wrote:
>>>
>>>> 1. A slab page will not be freed until the entire page is free (all
>>>> slabs have been kfree'd so to speak). Normal reclaim will definitely
>>>> free this page, but a lot of it depends on how frequently we are
>>>> scanning the LRU list and when this page got added.
>>>>
>>> You don't have to be freeing entire slab pages for the reclaim to have
>>> been useful. You could just be making space so that _future_
>>> allocations fill in the slab holes you just created. You may not be
>>> freeing pages, but you're reducing future system pressure.
>>>
>> Depends. If you've evicted something that will be referenced soon,
>> you're increasing system pressure.
>>
>>
> I don't think slab pages care about being referenced soon, they are
> either allocated or freed. A page is just a storage unit for the data
> structure. A new one can be allocated on demand.
>

If we're talking just about slab pages, I agree. If we're applying
pressure on the shrinkers, then you are removing live objects which can
be costly to reinstantiate.

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