linux-kernel - Re: [PATCH v10 00/16] Volatile Ranges v10

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Date:	Mon, 27 Jan 2014 16:42:27 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Minchan Kim <minchan@...nel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Dhaval Giani <dhaval.giani@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
	Andrea Righi <andrea@...terlinux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Mike Hommey <mh@...ndium.org>, Taras Glek <tglek@...illa.com>,
	Jan Kara <jack@...e.cz>, Rob Clark <robdclark@...il.com>,
	Jason Evans <je@...com>, pliard@...gle.com
Subject: Re: [PATCH v10 00/16] Volatile Ranges v10

On 01/27/2014 04:12 PM, Minchan Kim wrote:
> On Mon, Jan 27, 2014 at 05:23:17PM -0500, KOSAKI Motohiro wrote:
>> - Your number only claimed the effectiveness anon vrange, but not file vrange.
> Yes. It's really problem as I said.
> From the beginning, John Stultz wanted to promote vrange-file to replace
> android's ashmem and when I heard usecase of vrange-file, it does make sense
> to me so that's why I'd like to unify them in a same interface.
>
> But the problem is lack of interesting from others and lack of time to
> test/evaluate it. I'm not an expert of userspace so actually I need a bit
> help from them who require the feature but at a moment,
> but I don't know who really want or/and help it.
>
> Even, Android folks didn't have any interest on vrange-file.

Just as a correction here. I really don't think this is the case, as
Android's use definitely relies on file based volatility. It might be
more fair to say there hasn't been very much discussion from Android
developers on the particulars of the file volatility semantics (out
possibly not having any particular objections, or more-likely, being a
bit too busy to follow the all various theoretical tangents we've
discussed).

But I'd not want anyone to get the impression that anonymous-only
volatility would be sufficient for Android's needs.


(And to further clarify here, since this can be confusing... 
shmem/tmpfs-only file volatility *would* be sufficient, despite that
technically being anonymous backed memory. The key issue is we need to
be able to share the volatility between processes.)


> So, we might drop vrange-file part in this patchset if it's really headache.
> But let's discuss further because still I believe it's valuable feature to
> keep instead of dropping.

If it helps gets interest in reviewing this, I'm ok with deferring
(tmpfs) file volatility, so folks can get comfortable with anonymous
volatility. But I worry its too critical a feature to ignore.

thanks
-john

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