linux-kernel - Re: [RFC][PATCH 0/5] VM

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Date:	Tue, 27 May 2014 11:56:44 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Konstantin Khlebnikov <koct9i@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Mike Marciniszyn <infinipath@...el.com>
Subject: Re: [RFC][PATCH 0/5] VM_PINNED

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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