Messages in this thread | | | Date | Tue, 3 Aug 2010 09:15:13 +0530 | From | Balbir Singh <> | Subject | Re: [PATCH -mm 2/5] use ID in page cgroup |
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* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-08-02 19:14:10]:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > 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@jp.fujitsu.com> > --- > 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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