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	Original line	Diff line number	Diff line
	@@ -394,6 +394,14 @@ config CGROUP_MEM_CONT
	Provides a memory controller that manages both page cache and		Provides a memory controller that manages both page cache and
	RSS memory.		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		config PROC_PID_CPUSET
	bool "Include legacy /proc/<pid>/cpuset file"		bool "Include legacy /proc/<pid>/cpuset file"
	depends on CPUSETS		depends on CPUSETS