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Date: Thu, 03 Jul 2014 08:41:33 -0700
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Subject: Re: [Qemu-devel] [PATCH 00/10] RFC: userfault
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To: Andrea Arcangeli <aarcange@redhat.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Robert Love <rlove@google.com>, Jan Kara <jack@suse.cz>, Neil Brown <neilb@suse.de>, Stefan Hajnoczi <stefanha@gmail.com>, Andrew Jones <drjones@redhat.com>, KOSAKI Motohiro <kosaki.motohiro@gmail.com>, Michel Lespinasse <walken@google.com>, Taras Glek <tglek@mozilla.com>, Juan Quintela <quintela@redhat.com>, Hugh Dickins <hughd@google.com>, Isaku Yamahata <yamahata@valinux.co.jp>, Mel Gorman <mgorman@suse.de>, Android Kernel Team <kernel-team@android.com>, Mel Gorman <mel@csn.ul.ie>, "\"Dr. David Alan Gilbert\"" <dgilbert@redhat.com>, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>, Anthony Liguori <anthony@codemonkey.ws>, Mike Hommey <mh@glandium.org>, Keith Packard <keithp@keithp.com>, Wenchao Xia <wenchaoqemu@gmail.com>, Minchan Kim <minchan@kernel.org>, Dmitry Adamushko <dmitry.adamushko@gmail.com>, Johannes Weiner <hannes@cmpxchg.org>, Paolo Bonzini <pbonzini@redhat.com>, Andrew Morton <akpm@linux-foundation.org>

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.