linux-kernel - Re: [PATCH -mm 3/6] ksm: fix ksm swapin time optimization

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Message-ID: <20100623174718.GD16195@random.random>
Date:	Wed, 23 Jun 2010 19:47:18 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	linux-mm@...ck.org, avi@...hat.com
Subject: Re: [PATCH -mm 3/6] ksm: fix ksm swapin time optimization

On Mon, Jun 21, 2010 at 04:34:39PM -0400, Rik van Riel wrote:
> From: Andrea Arcangeli <aarcange@...hat.com>
> Subject: fix ksm swapin time optimization
> 
> The new anon-vma code, was suboptimal and it lead to erratic invocation of
> ksm_does_need_to_copy. That leads to host hangs or guest vnc lockup, or weird
> behavior.  It's unclear why ksm_does_need_to_copy is unstable but the point is
> that when KSM is not in use, ksm_does_need_to_copy must never run or we bounce

BTW, I'm debugging why ksm_does_need_to_copy breaks things... probably
I found something already, maybe not. I'll let you know as soon as I
have a fix. In the meantime the one above is a fix needed to avoid
calling ksm_does_need_to_copy erratically even when KSM is off (which
also avoids the bug to trigger).
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