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

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Message-ID: <alpine.DEB.2.00.1206291526180.15200@chino.kir.corp.google.com>
Date:	Fri, 29 Jun 2012 15:30:28 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>
cc:	Petr Holasek <pholasek@...hat.com>,
	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:

> > 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.
> 
> Oh, I should have checked the archives given that it's v2.  I expected
> it to get complex but didn't put enough thought into it to see /that/
> amount of complexity.  Sorry.
> 
> Carry on, then :-)
> 

I don't think it's an unfair amount of complexity to ask for, and I don't 
see the problem with ksm merging two pages that have a distance under the 
configured threshold and leaving the third page unmerged; by configuring 
the threshold (which should be a char, not an int) the admin has specified 
the locality that is necessary for optimal performance so has knowingly 
restricted ksm in that way.

I'd rename it to ksm_merge_distance, which is more similar to 
reclaim_distance, and return to the first version of this patch.
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