Messages in this thread | | | Subject | Re: [PATCH] mm: memcg/slab: optimize objcg stock draining | From | Imran Khan <> | Date | Wed, 6 Jan 2021 17:19:33 +1100 |
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On 6/1/21 3:22 pm, Roman Gushchin wrote: > Imran Khan reported a regression in hackbench results caused by the > commit f2fe7b09a52b ("mm: memcg/slab: charge individual slab objects > instead of pages"). The regression is noticeable in the case of > a consequent allocation of several relatively large slab objects, > e.g. skb's. As soon as the amount of stocked bytes exceeds PAGE_SIZE, > drain_obj_stock() and __memcg_kmem_uncharge() are called, and it leads > to a number of atomic operations in page_counter_uncharge(). > > The corresponding call graph is below (provided by Imran Khan): > |__alloc_skb > | | > | |__kmalloc_reserve.isra.61 > | | | > | | |__kmalloc_node_track_caller > | | | | > | | | |slab_pre_alloc_hook.constprop.88 > | | | obj_cgroup_charge > | | | | | > | | | | |__memcg_kmem_charge > | | | | | | > | | | | | |page_counter_try_charge > | | | | | > | | | | |refill_obj_stock > | | | | | | > | | | | | |drain_obj_stock.isra.68 > | | | | | | | > | | | | | | |__memcg_kmem_uncharge > | | | | | | | | > | | | | | | | |page_counter_uncharge > | | | | | | | | | > | | | | | | | | |page_counter_cancel > | | | | > | | | | > | | | |__slab_alloc > | | | | | > | | | | |___slab_alloc > | | | | | > | | | |slab_post_alloc_hook > > Instead of directly uncharging the accounted kernel memory, it's > possible to refill the generic page-sized per-cpu stock instead. > It's a much faster operation, especially on a default hierarchy. > As a bonus, __memcg_kmem_uncharge_page() will also get faster, > so the freeing of page-sized kernel allocations (e.g. large kmallocs) > will become faster. > > A similar change has been done earlier for the socket memory by > the commit 475d0487a2ad ("mm: memcontrol: use per-cpu stocks for > socket memory uncharging"). > > Signed-off-by: Roman Gushchin <guro@fb.com> > Reported-by: Imran Khan <imran.f.khan@oracle.com>
Tested-by: Imran Khan <imran.f.khan@oracle.com>
> --- > mm/memcontrol.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0d74b80fa4de..8148c1df3aff 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3122,9 +3122,7 @@ void __memcg_kmem_uncharge(struct mem_cgroup *memcg, unsigned int nr_pages) > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) > page_counter_uncharge(&memcg->kmem, nr_pages); > > - page_counter_uncharge(&memcg->memory, nr_pages); > - if (do_memsw_account()) > - page_counter_uncharge(&memcg->memsw, nr_pages); > + refill_stock(memcg, nr_pages); > } > > /** >
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