Messages in this thread | | | Date | Wed, 22 Oct 2014 18:11:40 +0200 | From | Michal Hocko <> | Subject | Re: [patch 4/4] mm: memcontrol: remove unnecessary PCG_USED pc->mem_cgroup valid flag |
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On Mon 20-10-14 11:22:12, Johannes Weiner wrote: > pc->mem_cgroup had to be left intact after uncharge for the final LRU > removal, and !PCG_USED indicated whether the page was uncharged. But > since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") pages are > uncharged after the final LRU removal. Uncharge can simply clear the > pointer and the PCG_USED/PageCgroupUsed sites can test that instead. > > Because this is the last page_cgroup flag, this patch reduces the > memcg per-page overhead to a single pointer.
Nice. I have an old patch which stuck this flag into page_cgroup pointer but this is of course much much better!
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Just a nit below
[...] > @@ -2525,9 +2523,10 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
memcg = NULL initialization is not needed now
> VM_BUG_ON_PAGE(!PageLocked(page), page); > > pc = lookup_page_cgroup(page); > - if (PageCgroupUsed(pc)) { > - memcg = pc->mem_cgroup; > - if (memcg && !css_tryget_online(&memcg->css)) > + memcg = pc->mem_cgroup; > + > + if (memcg) { > + if (!css_tryget_online(&memcg->css)) > memcg = NULL; > } else if (PageSwapCache(page)) { > ent.val = page_private(page);
> #else > static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg) [...] -- Michal Hocko SUSE Labs
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