linux-kernel - Re: [patch 1/3] mm: decouple unevictable lru from mmu

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Message-ID: <12087.1237805305@redhat.com>
Date:	Mon, 23 Mar 2009 10:48:25 +0000
From:	David Howells <dhowells@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	dhowells@...hat.com,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.com>,
	MinChan Kim <minchan.kim@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>
Subject: Re: [patch 1/3] mm: decouple unevictable lru from mmu

Johannes Weiner <hannes@...xchg.org> wrote:

> David, why do we need two Kconfig symbols for mlock and the mlock page
> bit?  Don't we always provide mlock on mmu and never on nommu?

Because whilst the PG_mlocked doesn't exist if we don't have mlock() because
we're in NOMMU mode, that does not imply that it _does_ exist if we _do_ have
mlock() as it's also contingent on having the unevictable LRU.

Not only that, CONFIG_HAVE_MLOCK used in mm/internal.h to switch some stuff
out based on whether we have mlock() available or not - which is not the same
as whether we have PG_mlocked or not.

Mainly I thought it made the train of logic easier.

Note that neither symbol is actually manually adjustable.

David
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