linux-kernel - Re: [PATCH v4] KSM: numa awareness sysfs knob

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Message-ID: <5064748A.4020509@redhat.com>
Date:	Thu, 27 Sep 2012 11:45:14 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Petr Holasek <pholasek@...hat.com>
CC:	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Anton Arapov <anton@...hat.com>
Subject: Re: [PATCH v4] KSM: numa awareness sysfs knob

On 09/23/2012 08:56 PM, Petr Holasek wrote:
> Introduces new sysfs boolean knob /sys/kernel/mm/ksm/merge_across_nodes
> which control merging pages across different numa nodes.
> When it is set to zero only pages from the same node are merged,
> otherwise pages from all nodes can be merged together (default behavior).
>
> Typical use-case could be a lot of KVM guests on NUMA machine
> and cpus from more distant nodes would have significant increase
> of access latency to the merged ksm page. Sysfs knob was choosen
> for higher variability when some users still prefers higher amount
> of saved physical memory regardless of access latency.
>
> Every numa node has its own stable & unstable trees because of faster
> searching and inserting. Changing of merge_nodes value is possible only
> when there are not any ksm shared pages in system.
>
> I've tested this patch on numa machines with 2, 4 and 8 nodes and
> measured speed of memory access inside of KVM guests with memory pinned
> to one of nodes with this benchmark:

Acked-by: Rik van Riel <riel@...hat.com>

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