linux-kernel - Re: [RFC][PATCH] Anonymous shared memory (ashmem) subsystem

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Message-ID: <CAF_S4t_oOwsuPJdMXv+wPVhzecUag=TOWj1-KtFJqYUZOCBbog@mail.gmail.com>
Date:	Mon, 18 Jul 2011 23:32:42 -0400
From:	Bryan Donlan <bdonlan@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Robert Love <rlove@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Eric Anholt <eric@...olt.net>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [RFC][PATCH] Anonymous shared memory (ashmem) subsystem

On Mon, Jul 18, 2011 at 22:19, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Jul 18, 2011 at 11:54:34AM -0700, John Stultz wrote:
>> From: Robert Love <rlove@...gle.com>
>>
>> Recently, Robert Love updated his ashmem patch and posted it here:
>>       http://www.kernel.org/pub/linux/kernel/people/rml/ashmem/
>>
>> This reminded me that in all the conversations around the Android patches,
>> I've not seen any discussion on lkml about the ashmem functionality.
>> Coming from Robert, its very clean and self-contained and seems pretty
>> interesting. So I wanted to send it out for review and comments.
>
> And utterly stupid, just use tmpfs and /dev/zero for the base functionality.
>
> And the pinning crap really needs a much better rationale.

The pinning stuff seems like a reasonable idea to me, but why should
it be limited to ashmem using a private ioctl? If it were a proper
syscall, I could see automatic discarding being useful in on-disk
filesystems as well, for managing persistent caches. But yes, tmpfs
already solved the problem of getting a shared-memory file descriptor
- just open a random-name file in tmpfs, unlink it, and start passing
it around.
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