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Subject: Re: Allow migration of mlocked page?
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 14 May 2012 16:08:57 +0200
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References: <4FAC9786.9060200@kernel.org> <20120511131404.GQ11435@suse.de>
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To: Mel Gorman <mgorman@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>, Minchan Kim <minchan@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, Rik van Riel <riel@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, tglx@linutronix.de, Ingo Molnar <mingo@redhat.com>, Theodore Ts'o <tytso@mit.edu>


Anyway, afaict there's only two options:

 1) make mlock() mean physically pinned (which we've so far always
rejected and isn't supported by whatever passes as a std for unix -- at
least not by the precise wording).

 2) keep mlock() to mean no major fault.

I strongly prefer 2 -- its what we've always said.


This might mean there's a need for a stronger API -- one that also
guarantees physically pinned. This is a more expensive
resource/operation. It means we need to migrate all memory to UNMOVABLE
blocks, possibly growing the number of such blocks with all the
down-sides that has.

Alternatively -- in case we pick 1 -- we should create a weaker variant
that does what mlock means now in order to allow people to not pressure
the system unduly.=20

I don't see any other way.. the current constraints really are mutually
exclusive.

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