linux-kernel - Re: [PATCH v2] KSM: numa awareness sysfs knob

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Message-ID: <20120629163033.GA11327@stainedmachine.redhat.com>
Date:	Fri, 29 Jun 2012 18:30:33 +0200
From:	Petr Holasek <pholasek@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Anton Arapov <anton@...hat.com>
Subject: Re: [PATCH v2] KSM: numa awareness sysfs knob

On Fri, 29 Jun 2012, Johannes Weiner wrote:
> On Fri, Jun 29, 2012 at 01:49:52PM +0200, Petr Holasek wrote:
> > Introduces new sysfs boolean knob /sys/kernel/mm/ksm/merge_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).
> 
> Is it conceivable that admins may (in the future) want to merge only
> across nodes that are below a given distance threshold?
> 
> I'm not asking to implement this, just whether the knob can be
> introduced such that it's future-compatible.  Make it default to a
> Very High Number and only allow setting it to 0 for now e.g.?  And
> name it max_node_merge_distance (I'm bad at names)?
> 
> What do you think?

I started with exactly same idea as you described above in the first
RFC, link: https://lkml.org/lkml/2011/11/30/91
But this approach turned out to be more complicated than it looked
(see two last emails in thread) and complexity of solution would rise
a lot.

Regards,
Petr H
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