linux-kernel - Re: [PATCH] mm: munlock use mapcount to avoid terrible overhead

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Message-ID: <alpine.LSU.2.00.1110181752440.4283@sister.anvils>
Date:	Tue, 18 Oct 2011 17:56:23 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Michel Lespinasse <walken@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: munlock use mapcount to avoid terrible overhead

On Tue, 18 Oct 2011, Andrew Morton wrote:
> On Tue, 18 Oct 2011 17:02:56 -0700 (PDT)
> Hugh Dickins <hughd@...gle.com> wrote:
> 
> > A process spent 30 minutes exiting, just munlocking the pages of a large
> > anonymous area that had been alternately mprotected into page-sized vmas:
> > for every single page there's an anon_vma walk through all the other
> > little vmas to find the right one.
> 
> And how long did the test case take with the patch applied?

5 seconds in the case tried; but the issue is quadratic,
so you can make the improvement look arbitrarily good.

Hugh
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