Re: [RFC][PATCH 2/3] memcg: reduce size of struct page_cgroup.

[Michal Hocko <mhocko@suse.cz>]

On Mon 19-03-12 17:01:27, KAMEZAWA Hiroyuki wrote:
> Now, page_cgroup->flags has only 3bits. Considering alignment of
> struct mem_cgroup, which is allocated by kmalloc(), we can encode
> pointer to mem_cgroup and flags into a word.
                                  into a single word.

> 
> After this patch, pc->flags is encoded as
> 
>  63                           2     0
>   | pointer to memcg..........|flags|

Looks good.
Acked-by: Michal Hocko <mhocko@suse.cz>

> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  include/linux/page_cgroup.h |   15 ++++++++++++---
>  1 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 92768cb..bca5447 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -1,6 +1,10 @@
>  #ifndef __LINUX_PAGE_CGROUP_H
>  #define __LINUX_PAGE_CGROUP_H
>  
> +/*
> + * Because these flags are encoded into ->flags with a pointer,
> + * we cannot have too much flags.
                     ^^^^^^^^^^^^^^ 
cannot have too many flags 
but an explicit BUILD_BUG_ON would be much more precise than a comment I
guess.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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