Re: [PATCH] Document Linux Memory Policy

[glebn@voltaire.com (Gleb Natapov)]

On Wed, May 30, 2007 at 11:41:25PM -0700, Christoph Lameter wrote:
> On Thu, 31 May 2007, Gleb Natapov wrote:
> 
> > On Wed, May 30, 2007 at 10:56:17AM -0700, Christoph Lameter wrote:
> > > > You don't get COW if it's a shared mapping.  You use the page cache
> > > > pages which ignores my mbind().  That's my beef!  [;-)]
> > > 
> > > page cache pages are subject to a tasks memory policy regardless of how we 
> > > get to the page cache page. I think that is pretty consistent.
> > > 
> > I am a little bit confused here. If two processes mmap some file with
> > MAP_SHARED and each one marks different part of the file with
> > numa_setlocal_memory() (and suppose that no pages were faulted in for
> 
> The numa_setlocal_memory() has no effect on ranges that map pagecache 
> pages.
> 
> > this file yet). Now first process touches a part of the file that was
> > marked local by second process. Will faulted page  be placed in first
> > process' local memory or second? I surely expect later, but it seems I
> > am wrong.
> 
> The faulted page will use the memory policy of the task that faulted it 
> in. If that process has numa_set_localalloc() set then the page will be 
> located as closely as possible to the allocating thread.

Thanks. But I have to say this feels very unnatural. So to have
desirable effect I have to create shared memory with shmget?

--
			Gleb.

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