lkml.org 
[lkml]   [2008]   [Feb]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] Document huge memory/cache overhead of memory controller in Kconfig
Document huge memory/cache overhead of memory controller in Kconfig

I was a little surprised that 2.6.25-rc* increased struct page for the memory
controller. At least on many x86-64 machines it will not fit into a single
cache line now anymore and also costs considerable amounts of RAM.
At earlier review I remembered asking for a external data structure for this.

It's also quite unobvious that a innocent looking Kconfig option with a
single line Kconfig description has such a negative effect.

This patch attempts to document these disadvantages at least so that users
configuring their kernel can make a informed decision.

Cc: balbir@linux.vnet.ibm.com

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux/init/Kconfig
===================================================================
--- linux.orig/init/Kconfig
+++ linux/init/Kconfig
@@ -394,6 +394,14 @@ config CGROUP_MEM_CONT
Provides a memory controller that manages both page cache and
RSS memory.

+ Note that setting this option increases fixed memory overhead
+ associated with each page of memory in the system by 4/8 bytes
+ and also increases cache misses because struct page on many 64bit
+ systems will not fit into a single cache line anymore.
+
+ Only enable when you're ok with these trade offs and really
+ sure you need the memory controller.
+
config PROC_PID_CPUSET
bool "Include legacy /proc/<pid>/cpuset file"
depends on CPUSETS

\
 
 \ /
  Last update: 2008-02-20 13:27    [W:0.633 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site