On Sat, Feb 23, 2008 at 1:02 PM, <[EMAIL PROTECTED]> wrote:
>
> The patch titled
> cgroup memory controller: document huge memory/cache overhead in Kconfig
> has been added to the -mm tree. Its filename is
>
> cgroup-memory-controller-document-huge-memory-cache-overhead-in-kconfig.patch
>
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>
> ------------------------------------------------------
> Subject: cgroup memory controller: document huge memory/cache overhead in
> Kconfig
> From: Andi Kleen <[EMAIL PROTECTED]>
>
> 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]>
> ---
>
> init/Kconfig | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff -puN
> init/Kconfig~cgroup-memory-controller-document-huge-memory-cache-overhead-in-kconfig
> init/Kconfig
> ---
> a/init/Kconfig~cgroup-memory-controller-document-huge-memory-cache-overhead-in-kconfig
> +++ a/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.
> +
Andrew,
I asked Andi what architectures have a cacheline size such that 56
bytes would fit in the cache, but 64 bytes would not. I have not heard
back. I would like Andi's approval to change the text to
Note that setting this option increases fixed memory overhead
associated with each page of memory in the system by 4/8 bytes
Only enable when you're ok with these trade offs and really
sure you need the memory controller.
Andi, please confirm at the earliest.
Balbir
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