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 <[email protected]> Cc: Balbir Singh <[email protected]> Acked-by: Paul Menage <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
kyagi · Feb 24, 2008 · 0835ab5 · 0835ab5
1 parent 00d6296
commit 0835ab5
Showing 1 changed file with 8 additions and 0 deletions.
diff --git a/init/Kconfig b/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