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

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Message-ID: <20110719033602.GA4867@infradead.org>
Date:	Mon, 18 Jul 2011 23:36:02 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Bryan Donlan <bdonlan@...il.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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 11:32:42PM -0400, Bryan Donlan wrote:
> 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.

Exactly.

> 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.

Indeed.  And as mentioned before using /dev/zero as the file will
get you a pre-unlinked tmpfs fd without any races, and without the
need of actually mounting shmem into any namespace.
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