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

[Nick Piggin]

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.

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