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

From: Nick Piggin
Date: Fri Mar 12 2004 - 18:09:55 EST

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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