Re: [PATCH] vmscan: evict use-once pages first (v2)

[Wu Fengguang]

On Sun, May 03, 2009 at 11:24:03AM +0800, Rik van Riel wrote:
> On Sun, 3 May 2009 11:15:39 +0800
> Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> 
> > Commit 7e9cd484204f(vmscan: fix pagecache reclaim referenced bit
> > check) tries to address scalability problem when every page get
> > mapped and referenced, so that logic(which lowed the priority of
> > mapped pages) could be enabled only on conditions like (priority <
> > DEF_PRIORITY).
> > 
> > Or preferably we can explicitly protect the mapped executables,
> > as illustrated by this patch (a quick prototype).
> 
> Over time, given enough streaming IO and idle applications,
> executables will still be evicted with just this patch.
> 
> However, a combination of your patch and mine might do the
> trick.  I suspect that executables are never a very big
> part of memory, except on small memory systems, so protecting
> just the mapped executables should not be a scalability
> problem.

Yes, that's my intent to take advantage of you patch :-)

There may be programs that embed large amount of static data with
them - think about self-decompression data - but that's fine: this
patch behaves not in a too persistent way. Plus we can apply a size
limit(say 100M) if necessary.

> My patch in combination with your patch should make sure
> that if something gets evicted from the active list, it's
> not executables - meanwhile, lots of the time streaming
> IO will completely leave the active file list alone.
 
They together make
- mapped executable pages the first class citizen;
- streaming IO least intrusive.

I think that would make most desktop users and server administrators
contented and comfortable :-)

Thanks,
Fengguang

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