Re: [PATCH] 2.6.4-rc2-mm1: vm-split-active-lists

[Nick Piggin <piggin@cyberone.com.au>]

Nikita Danilov wrote:

>Nick Piggin writes:
>
> > With my patch though, it gives unmapped pages the same treatment as
> > mapped pages. Without my patch, pages getting a lot of mark_page_accessed
> > activity can easily be promoted unfairly past mapped ones which are simply
> > getting activity through the pte.
>
>Another way to put it is that treatment of file system pages is dumbed
>down to the level of mapped ones: information about access patterns is
>just discarded.
>
>

In a way, yes.

> > 
> > I say just set the bit and let the scanner handle it.
>
>I think that decisions about balancing VM and file system caches should
>be done by higher level, rather than by forcing file system to use
>low-level mechanisms designed for VM, where only limited information is
>provided by hardware. Splitting page queues is a step in a right
>direction, as it allows to implement more precise replacement for the
>file system cache.
>
>

It makes it that much harder to calculate the pressure you are putting
on mapped vs unmapped pages though.