linux-kernel - Re: [PATCH 2/5] mempolicy: Remove mempolicy sharing

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Date:	Mon, 20 Aug 2012 19:35:14 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mgorman@...e.de>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Jones <davej@...hat.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Andi Kleen <ak@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 2/5] mempolicy: Remove mempolicy sharing

On Mon, 20 Aug 2012, Mel Gorman wrote:

> Ideally, the shared policy handling would be rewritten to either properly
> handle COW of the policy structures or at least reference count MPOL_F_SHARED
> based exclusively on information within the policy.  However, this patch takes
> the easier approach of disabling any policy sharing between VMAs. Each new
> range allocated with sp_alloc will allocate a new policy, set the reference
> count to 1 and drop the reference count of the old policy. This increases
> the memory footprint but is not expected to be a major problem as mbind()
> is unlikely to be used for fine-grained ranges. It is also inefficient
> because it means we allocate a new policy even in cases where mbind_range()
> could use the new_policy passed to it. However, it is more straight-forward
> and the change should be invisible to the user.


Hmmm. I dont like the additional memory use but this is definitely an
issue that needs addressing.

Reviewed-by: Christoph Lameter <cl@...ux.com>
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