linux-kernel - virtio ring cleanups, which save stack on older gcc

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Date:	Thu, 29 May 2014 16:56:41 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Jens Axboe <axboe@...nel.dk>, Minchan Kim <minchan@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: virtio ring cleanups, which save stack on older gcc

They don't make much difference: the easier fix is use gcc 4.8
which drops stack required across virtio block's virtio_queue_rq
down to that kmalloc in virtio_ring from 528 to 392 bytes.

Still, these (*lightly tested*) patches reduce to 432 bytes,
even for gcc 4.6.4.  Posted here FYI.

Cheers,
Rusty.

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