Commit 0835ab53 authored Feb 23, 2008 by Andi Kleen Committed by Linus Torvalds Feb 23, 2008

cgroup memory controller: document huge memory/cache overhead 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.

Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 00d62961

init/Kconfig

+8 −0

Original line number	Diff line number	Diff line
		@@ -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