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@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
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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