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Date: Tue, 27 May 2014 11:56:44 -0500 (CDT)
From: Christoph Lameter <cl@gentwo.org>
Subject: Re: [RFC][PATCH 0/5] VM_PINNED
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Sender: owner-linux-mm@kvack.org
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Andrew Morton <akpm@linux-foundation.org>, Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>, Roland Dreier <roland@kernel.org>, Sean Hefty <sean.hefty@intel.com>, Hal Rosenstock <hal.rosenstock@gmail.com>, Mike Marciniszyn <infinipath@intel.com>

On Tue, 27 May 2014, Peter Zijlstra wrote:

> > Code could be easily added to alloc_pages_vma() to consider the pinned
> > status on allocation. Remove GFP_MOVABLE if the vma is pinned.
>
> Yes, but alloc_pages_vma() isn't used for shared pages (with exception
> of shmem and hugetlbfs).

alloc_pages_vma() is used for all paths where we populate address ranges
with pages. This is what we are doing when pinning. Pages are not
allocated outside of a vma context.

What do you mean by shared pages that are not shmem pages? AnonPages that
are referenced from multiple processes?

> So whichever way around we have to do the mm_populate() + eviction hook
> + migration code, and since that equally covers the anon case, why
> bother?

Migration is expensive and the memory registration overhead already
causes lots of complaints.

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