linux-kernel - Re: [PATCH] Physical Memory Management [0/1]

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Message-Id: <1242321000.6642.1456.camel@laptop>
Date:	Thu, 14 May 2009 19:10:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Micha__ Nazarewicz <m.nazarewicz@...sung.com>,
	linux-kernel@...r.kernel.org, m.szyprowski@...sung.com,
	kyungmin.park@...sung.com, linux-mm@...ck.org
Subject: Re: [PATCH] Physical Memory Management [0/1]

On Thu, 2009-05-14 at 10:07 -0700, Andrew Morton wrote:
> On Thu, 14 May 2009 15:04:55 +0200
> Micha__ Nazarewicz <m.nazarewicz@...sung.com> wrote:
> 
> > On Thu, 14 May 2009 14:05:02 +0200, Peter Zijlstra wrote:
> > > And who says your pre-allocated pool won't fragment with repeated PMM
> > > use?
> > 
> > Yes, this is a good question.  What's more, there's no good answer. ;)
> > 
> 
> We do have capability in page reclaim to deliberately free up
> physically contiguous pages (known as "lumpy reclaim").
> 
> It would be interesting were someone to have a go at making that
> available to userspace: ask the kernel to give you 1MB of physically
> contiguous memory.  There are reasons why this can fail, but migrating
> pages can be used to improve the success rate, and userspace can be
> careful to not go nuts using mlock(), etc.
> 
> The returned memory would of course need to be protected from other
> reclaim/migration/etc activity.

I thought we already exposed this, its called hugetlbfs ;-)

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