Re: mapped pagecache pages vs unmapped pages

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

On 04/09/2012 08:31 PM, Minchan Kim wrote:
> 2012-04-10 i??i ? 8:50, Alexey Ivanov i?' e,?:
>
>> Did you consider making this ratio tunable, at least manually(i.e. via sysctl)?
>> I suppose we are not the only ones with almost-whole-ram-mmaped workload.
>
> Personally, I think it's not good approach.
> It depends on kernel's internal implemenatation which would be changed
> in future as we chagend it at 2.6.28.

I also believe that a tunable for this is not going to be
a very workable approach, for the simple reason that changing
the value does not make a predictable change in the effectiveness
of working set detection or protection.

> In my opinion, kernel just should do best effort to keep active working
> set except some critical pages which are code pages.

Johannes has some experimental code to measure refaults, and
calculate their distance in a multi-zone, multi-cgroup environment.

That would allow us to predictably place things in the working set
as required.

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