Messages in this thread | | | Date | Thu, 23 Feb 2012 17:57:04 +0400 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH 1/2] memcg: fix page_referencies cgroup filter on global reclaim |
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Johannes Weiner wrote: > On Tue, Feb 21, 2012 at 03:38:04PM +0400, Konstantin Khlebnikov wrote: >> Johannes Weiner wrote: >>> On Wed, Feb 15, 2012 at 08:28:30PM +0400, Konstantin Khlebnikov wrote: >>>> Global memory reclaimer should't skip referencies for any pages, >>>> even if they are shared between different cgroups. >>> >>> Agreed: if we reclaim from one memcg because of its limit, we want to >>> reclaim those pages that this group is not using. If it's used by >>> someone else, it should be evicted and refaulted by the group that >>> needs it. >>> >>> If we reclaim globally, all references are "true" because we want to >>> evict those pages that are not used by any cgroup. >>> >>> But if we reclaim a hierarchical subgroup, we don't want to evict >>> pages that are shared among this hierarchy, either, even if the memcg >>> that has the page charged to it is not using it. Bouncing the page >>> around the hierarchy is not sensible, because it does not solve the >>> problem of the parent hitting its limit when the sibling group will >>> refault it in a blink of an eye. It should only be evicted if the >>> memcg that's not using it nears its own limit, because only in that >>> case would reclaiming the page remedy the situation. >>> >>>> This patch adds scan_control->current_mem_cgroup, which points to currently >>>> shrinking sub-cgroup in hierarchy, at global reclaim it always NULL. >>> >>> So to be consistent, I'm wondering if we should pass >>> sc->target_mem_cgroup - the limit-hitting hierarchy root - to >>> page_referenced() and then have mm_match_cgroup() do a >>> mem_cgroup_same_or_subtree() check to see if the vma is in the >>> hierarchy rooted at sc->target_mem_cgroup. >>> >>> Global reclaim is handled automatically, because mm_match_cgroup() is >>> not checked when the passed memcg is NULL, which sc->target_mem_cgroup >>> is for global reclaim. >> >> Also we can try to recharge page to other cgroup, if we found in rmap another its user >> outsize of currently shrinking hierarchy, page there is isolated, so at the end we will >> insert page directly to its lru. > > Not sure if it's worth the trouble, but that could work. > >> But the main purpose of this patch for me is killing mz->mem_cgroup dereference, >> because I plan to replace mz with direct reference to lruvec, which will be memcg-free object. > > I like that plan. How about this patch then?
I sent my version. See patch "[PATCH v3 02/21] memcg: make mm_match_cgroup() hirarchical"
one note below
> > --- > From: Johannes Weiner<hannes@cmpxchg.org> > Subject: mm: memcg: count pte references from every member of the reclaimed hierarchy > > 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. > > Reported-by: Konstantin Khlebnikov<khlebnikov@openvz.org> > Signed-off-by: Johannes Weiner<hannes@cmpxchg.org> > --- > include/linux/memcontrol.h | 3 ++- > mm/memcontrol.c | 2 +- > mm/vmscan.c | 6 ++++-- > 3 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 8537c5d..ba9455d 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -78,6 +78,7 @@ extern void mem_cgroup_uncharge_page(struct page *page); > 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); > +bool mem_cgroup_same_or_subtree(const struct mem_cgroup *, struct mem_cgroup *); > 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); > @@ -91,7 +92,7 @@ int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup) > rcu_read_lock(); > memcg = mem_cgroup_from_task(rcu_dereference((mm)->owner)); > rcu_read_unlock(); > - return cgroup == memcg; > + return mem_cgroup_same_or_subtree(cgroup, memcg); > }
seems like this memcg pointer is rcu-protected, so it seems broken.
> > extern struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *memcg); > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index e4be95a..f91d762 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1044,7 +1044,7 @@ struct lruvec *mem_cgroup_lru_move_lists(struct zone *zone, > * Checks whether given mem is same or in the root_mem_cgroup's > * hierarchy subtree > */ > -static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg, > +bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg, > struct mem_cgroup *memcg) > { > if (root_memcg != memcg) { > diff --git a/mm/vmscan.c b/mm/vmscan.c > index c631234..120646e 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -708,7 +708,8 @@ static enum page_references page_check_references(struct page *page, > int referenced_ptes, referenced_page; > unsigned long vm_flags; > > - referenced_ptes = page_referenced(page, 1, mz->mem_cgroup,&vm_flags); > + referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup, > + &vm_flags); > referenced_page = TestClearPageReferenced(page); > > /* Lumpy reclaim - ignore references */ > @@ -1710,7 +1711,8 @@ static void shrink_active_list(unsigned long nr_pages, > continue; > } > > - if (page_referenced(page, 0, mz->mem_cgroup,&vm_flags)) { > + if (page_referenced(page, 0, sc->target_mem_cgroup, > + &vm_flags)) { > nr_rotated += hpage_nr_pages(page); > /* > * Identify referenced, file-backed active pages and
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