linux-kernel - Re: [PATCH 00/10] RFC: userfault

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Date:	Thu, 03 Jul 2014 08:41:33 -0700
From:	Dave Hansen <dave@...1.net>
To:	Andrea Arcangeli <aarcange@...hat.com>, qemu-devel@...gnu.org,
	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
CC:	"\"Dr. David Alan Gilbert\"" <dgilbert@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Neil Brown <neilb@...e.de>, Mike Hommey <mh@...ndium.org>,
	Taras Glek <tglek@...illa.com>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Michel Lespinasse <walken@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Keith Packard <keithp@...thp.com>,
	"Huangpeng (Peter)" <peter.huangpeng@...wei.com>,
	Isaku Yamahata <yamahata@...inux.co.jp>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Stefan Hajnoczi <stefanha@...il.com>,
	Wenchao Xia <wenchaoqemu@...il.com>,
	Andrew Jones <drjones@...hat.com>,
	Juan Quintela <quintela@...hat.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 00/10] RFC: userfault

On 07/02/2014 09:50 AM, Andrea Arcangeli wrote:
> The MADV_USERFAULT feature should be generic enough that it can
> provide the userfaults to the Android volatile range feature too, on
> access of reclaimed volatile pages.

Maybe.

I certainly can't keep track of all the versions of the variations of
the volatile ranges patches.  But, I don't think it's a given that this
can be reused.  First of all, volatile ranges is trying to replace
ashmem and is going to require _some_ form of sharing.  This mechanism,
being tightly coupled to anonymous memory at the moment, is not a close
fit for that.

It's also important to call out that this is a VMA-based mechanism.  I
certainly can't predict what we'll merge for volatile ranges, but not
all of them are VMA-based.  We'd also need a mechanism on top of this to
differentiate plain not-present pages from not-present-because-purged pages.

That said, I _think_ this might fit well in to what the Mozilla guys
wanted out of volatile ranges.  I'm not confident about it, though.
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