linux-kernel - Re: [PATCH] mremap: skip page table lookup for non-faulted anonymous VMAs

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Message-ID: <20111107153220.GD3249@redhat.com>
Date:	Mon, 7 Nov 2011 16:32:20 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Nai Xia <nai.xia@...il.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Pawel Sikora <pluto@...k.net>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	jpiszcz@...idpixels.com, arekm@...-linux.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mremap: skip page table lookup for non-faulted anonymous
 VMAs

On Mon, Nov 07, 2011 at 12:21:35PM +0800, Nai Xia wrote:
> If an anonymous vma has not yet been faulted, move_page_tables() in move_vma()
> is not necessary for it.

I actually thought of adding that (in fact fork has it and it's more
likely to be beneficial for fork than for mremap I suspect), but this
adds a branch to the fast path for a case that shouldn't normally
materialize. So I don't think it's worth adding it as I expect it to
add overhead in average.
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