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: [EMAIL PROTECTED]
Signed-off-by: Andi Kleen <[EMAIL PROTECTED]>
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
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