Re: [patch 0/8] mm: thrash detection-based file cache sizing v5

[Rik van Riel <riel@redhat.com>]

On 10/21/2013 05:26 AM, Vlastimil Babka wrote:
> On 10/10/2013 11:46 PM, Johannes Weiner wrote:
>> Hi everyone,
>>
>> here is an update to the cache sizing patches for 3.13.
>>
>> 	Changes in this revision
>>
>> o Drop frequency synchronization between refaulted and demoted pages
>>    and just straight up activate refaulting pages whose access
>>    frequency indicates they could stay in memory.  This was suggested
>>    by Rik van Riel a looong time ago but misinterpretation of test
>>    results during early stages of development took me a while to
>>    overcome.  It's still the same overall concept, but a little simpler
>>    and with even faster cache adaptation.  Yay!
>
> Oh, I liked the previous approach with direct competition between the
> refaulted and demoted page :) Doesn't the new approach favor the
> refaulted page too much? No wonder it leads to faster cache adaptation,
> but could it also cause degradations for workloads that don't benefit
> from it? Were there any tests for performance regressions on workloads
> that were not the target of the patchset?

This is a good question, and one that is probably
best settled through experimentation.

Even with the first scheme (fault refaulted page to
the inactive list), those pages only need 2 accesses
to be promoted to the active list.

That is because a refault tends to immediately be
followed by an access (after all, the attempted
access causes the page to get loaded back into memory).

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