linux-kernel - Re: [PATCH 1/7] ksm: add some comments

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Message-ID: <alpine.LNX.2.00.1302221239450.6100@eggly.anvils>
Date:	Fri, 22 Feb 2013 12:50:25 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Ric Mason <ric.masonn@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Petr Holasek <pholasek@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/7] ksm: add some comments

On Fri, 22 Feb 2013, Ric Mason wrote:
> 
> What's the root reason merge_across_nodes setting just can be changed only
> when there are no ksm shared pages in system?

Simplicity.  Why add code (moving nodes from tree to tree, handling
the collisions) for a rare case that doesn't need to be fast?

> Can they be unmerged and merged again during ksmd scan?

That's more or less what happens, isn't it?  Perhaps you're
asking why the admin has to echo 2 >run; echo 0 >merge; echo 1 >run
instead of that all happening automatically inside the echo 0 > merge?

If I'd implemented it myself, I might have chosen to do it that way;
but neither I nor other reviewers felt strongly enough to change that,
though we could do so.

Hugh
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