Re: [PATCH] Document Linux Memory Policy

[Andi Kleen <ak@suse.de>]

On Friday 01 June 2007 11:38:03 Gleb Natapov wrote:
> On Thu, May 31, 2007 at 10:43:19PM +0200, Andi Kleen wrote:
> > 
> > > > > Do I
> > > > > miss something here?
> > > > 
> > > > I think you do.  
> > > OK. It seems I missed the fact that VMA policy is completely ignored for
> > > pagecache backed files and only task policy is used. 
> > 
> > That's not correct. tmpfs is page cache backed and supports (even shared) VMA policy.
> > hugetlbfs used to too, but lost its ability, but will hopefully get it again.
> > 
> This is even more confusing.

I see. Anything that doesn't work exactly as your particular 
application expects it is "unnatural" and "confusing". I suppose only
in Glebnix it would be different.

> So numa_*_memory() works different 
> depending on where file is created.

See it as "it doesn't work for files, but only for shared memory".
The main reason for that is that there is no way to make it persistent
for files.

I only objected to your page cache based description because tmpfs
(and even anonymous memory) are page cache based too.

> I can't rely on this anyway and 
> have to assume that numa_*_memory() call is ignored and prefault.

It's either use shared/anonymous memory or process policy.

> I think Lee's patches should be applied ASAP to fix this inconsistency.

They have serious semantic problems.

-Andi

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