On Tue, 24 Apr 2012 21:35:44 +0200
Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> The rmap walker checking page table references has historically
> ignored references from VMAs that were not part of the memcg that was
> being reclaimed during memcg hard limit reclaim.
>
> When transitioning global reclaim to memcg hierarchy reclaim, I missed
> that bit and now references from outside a memcg are ignored even
> during global reclaim.
>
> Reverting back to traditional behaviour - count all references during
> global reclaim and only mind references of the memcg being reclaimed
> during limit reclaim would be one option.
>
> However, the more generic idea is to ignore references exactly then
> when they are outside the hierarchy that is currently under reclaim;
> because only then will their reclamation be of any use to help the
> pressure situation. It makes no sense to ignore references from a
> sibling memcg and then evict a page that will be immediately refaulted
> by that sibling which contributes to the same usage of the common
> ancestor under reclaim.
>
> The solution: make the rmap walker ignore references from VMAs that
> are not part of the hierarchy that is being reclaimed.
>
> Flat limit reclaim will stay the same, hierarchical limit reclaim will
> mind the references only to pages that the hierarchy owns. Global
> reclaim, since it reclaims from all memcgs, will be fixed to regard
> all references.
>
> ...
>
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -78,6 +78,7 @@ extern void mem_cgroup_uncharge_cache_page(struct page *page);
>
> extern void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> int order);
> +bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *, struct mem_cgroup *);
I dunno about you guys, but this practice of omitting the names of the
arguments in the declaration drives me bats. It really does throw away
a *lot* of information. It looks OK when one is initially reading the
code, but when I actually go in there and do some work on the code, it
makes things significantly harder.
> int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg);
>
> extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
> @@ -91,10 +92,13 @@ static inline
> int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup)
> {
> struct mem_cgroup *memcg;
> + int match;
> +
> rcu_read_lock();
> memcg = mem_cgroup_from_task(rcu_dereference((mm)->owner));
> + match = memcg && __mem_cgroup_same_or_subtree(cgroup, memcg);
> rcu_read_unlock();
> - return cgroup == memcg;
> + return match;
> }
mm_match_cgroup() really wants to return a bool type, no?
> +bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> + struct mem_cgroup *memcg)
Like him.
> +static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
> + struct mem_cgroup *memcg)
And him.
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