* KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-08-02 19:14:10]:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> Now, addresses of memory cgroup can be calculated by their ID without complex.
> This patch relplaces pc->mem_cgroup from a pointer to a unsigned short.
> On 64bit architecture, this offers us more 6bytes room per page_cgroup.
> Use 2bytes for blkio-cgroup's page tracking. More 4bytes will be used for
> some light-weight concurrent access.
>
> We may able to move this id onto flags field but ...go step by step.
>
> Changelog: 20100730
> - fixed some garbage added by debug code in early stage
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> include/linux/page_cgroup.h | 3 ++-
> mm/memcontrol.c | 32 +++++++++++++++++++-------------
> mm/page_cgroup.c | 2 +-
> 3 files changed, 22 insertions(+), 15 deletions(-)
>
> Index: mmotm-0727/include/linux/page_cgroup.h
> ===================================================================
> --- mmotm-0727.orig/include/linux/page_cgroup.h
> +++ mmotm-0727/include/linux/page_cgroup.h
> @@ -12,7 +12,8 @@
> */
> struct page_cgroup {
> unsigned long flags;
> - struct mem_cgroup *mem_cgroup;
> + unsigned short mem_cgroup; /* ID of assigned memory cgroup */
> + unsigned short blk_cgroup; /* Not Used..but will be. */
> struct page *page;
> struct list_head lru; /* per cgroup LRU list */
> };
Can I recommend that on 64 bit systems, we merge the flag, mem_cgroup
and blk_cgroup into one 8 byte value. We could use
__attribute("packed") and do something like this
struct page_cgroup {
unsigned int flags;
unsigned short mem_cgroup;
unsigned short blk_cgroup;
...
} __attribute(("packed"));
Then we need to make sure we don't use more that 32 bits for flags,
which is very much under control at the moment.
This will save us 8 bytes in total on 64 bit systems and nothing on 32
bit systems, but will enable blkio cgroup to co-exist.
--
Three Cheers,
Balbir
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