From: Eric Wong <normalperson@yhbt.net>
Date: Tue, 30 Apr 2013 22:27:38 +0000 (-0700)
Subject: epoll: trim epitem by one cache line
X-Git-Tag: omap-for-v3.10/dt-fixes-for-merge-window~88^2~69
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=39732ca5af4b09f4db561149041ddad7211019a5;p=pandora-kernel.git

epoll: trim epitem by one cache line

It is common for epoll users to have thousands of epitems, so saving a
cache line on every allocation leads to large memory savings.

Since epitem allocations are cache-aligned, reducing sizeof(struct
epitem) from 136 bytes to 128 bytes will allow it to squeeze under a
cache line boundary on x86_64.

Via /sys/kernel/slab/eventpoll_epi, I see the following changes on my
x86_64 Core2 Duo (which has 64-byte cache alignment):

	object_size  :  192 => 128
	objs_per_slab:   21 =>  32

Also, add a BUILD_BUG_ON() to check for future accidental breakage.

[akpm@linux-foundation.org: use __packed, for all architectures]
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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