Andi Kleen wrote: > 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.
The size of struct page earlier was 56 bytes on x86_64 and with 64 bytes it won't fit into the cacheline anymore? Please also look at http://lwn.net/Articles/234974/ > 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. > + Looks good Acked-by: Balbir Singh <[EMAIL PROTECTED]> > config PROC_PID_CPUSET > bool "Include legacy /proc/<pid>/cpuset file" > depends on CPUSETS -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
