linux-kernel - [PATCH] io: remove padding from io

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Date:	Fri, 26 Feb 2010 12:56:00 +0000
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Jens Axboe <jens.axboe@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nikanth Karthikesan <knikanth@...e.de>,
	Jeff Moyer <jmoyer@...hat.com>, Vivek Goyal <vgoyal@...hat.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] io: remove padding from io_context on 64bit builds

On 64 bit builds when CONFIG_BLK_CGROUP=n (the default) this removes 8
bytes of padding from structure io_context and drops its size from 72 to
64 bytes, so needing one fewer cachelines and allowing more objects per
slab in it's kmem_cache.

Signed-off-by: Richard Kennedy <richard@....demon.co.uk>

----
patch against 2.6.33
compiled & test on x86_64 AMDX2
regards
Richard


diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 78ef023..1195a80 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -49,8 +49,8 @@ struct io_context {
 	/*
 	 * For request batching
 	 */
-	unsigned long last_waited; /* Time last woken after wait for request */
 	int nr_batch_requests;     /* Number of requests left in the batch */
+	unsigned long last_waited; /* Time last woken after wait for request */
 
 	struct radix_tree_root radix_root;
 	struct hlist_head cic_list;


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