linux-kernel - [PATCH] RCU : move three variables to __read

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Message-ID: <475E1726.1040908@cosmosbay.com>
Date:	Tue, 11 Dec 2007 05:50:46 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Dipankar Sarma <dipankar@...ibm.com>,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] RCU : move three variables to __read_mostly to save space

I noticed this vmlinux layout on i686 (where CONFIG_X86_L1_CACHE_SHIFT = 7) :

c06cdab4 d pid_caches_lh
c06cdb00 d qlowmark
c06cdb04 d qhimark
c06cdb08 d blimit
c06cdb80 d rcu_ctrlblk
c06cdc80 d rcu_bh_ctrlblk

This means that qlowmark, qhimark and blimit use a whole 128 bytes cache line. 
Linker is not smart enough for us.

Moving these three variables to read_mostly section saves 116 (128-12) bytes.

# size vmlinux vmlinux.before_patch
    text    data     bss     dec     hex filename
6343966  490818  630784 7465568  71ea60 vmlinux
6343966  490930  630784 7465680  71ead0 vmlinux.before_patch

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>

View attachment "rcu.patch" of type "text/plain" (611 bytes)