On Mon 13-05-13 13:05:24, Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@xxxxxxxxxx>
>
> Change the first argument of mem_cgroup_{update,inc,dec}_page_stat() from
> 'struct page *' to 'struct mem_cgroup *', and so move PageCgroupUsed(pc)
> checking out of mem_cgroup_update_page_stat(). This is a prepare patch for
> the following memcg page stat lock simplifying.
No, please do not do this because it just spreads memcg specific code
out of memcontrol.c. Besides that the patch is not correct.
[...]
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1109,12 +1109,24 @@ void page_add_file_rmap(struct page *page)
> {
> bool locked;
> unsigned long flags;
> + struct page_cgroup *pc;
> + struct mem_cgroup *memcg = NULL;
>
> mem_cgroup_begin_update_page_stat(page, &locked, &flags);
> + pc = lookup_page_cgroup(page);
> +
> + rcu_read_lock();
> + memcg = pc->mem_cgroup;
a) unnecessary RCU take for memcg disabled and b) worse KABOOM in that case
as page_cgroup is NULL. We really do not want to put
mem_cgroup_disabled() tests all over the place. The idea behind
mem_cgroup_begin_update_page_stat was to be almost a noop for !memcg
(and the real noop for !CONFIG_MEMCG).
so Nak to this approach
--
Michal Hocko
SUSE Labs
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