From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH v3 11/51] memcg: implement mem_cgroup_css_from_page() Date: Wed, 27 May 2015 13:57:26 -0400 Message-ID: <20150527175726.GQ7099@htj.duckdns.org> References: <1432329245-5844-1-git-send-email-tj@kernel.org> <1432329245-5844-12-git-send-email-tj@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, jack-AlSwsSmVLrQ@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, mhocko-AlSwsSmVLrQ@public.gmane.org, clm-b10kYP2dOMg@public.gmane.org, fengguang.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org, gthelen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, khlebnikov-XoJtRXgx1JseBXzfvpsJ4g@public.gmane.org To: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org Return-path: Content-Disposition: inline In-Reply-To: <1432329245-5844-12-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org >>From b8077b30ce147052a9e55632d80a3c22241a64be Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 27 May 2015 13:54:22 -0400 Implement mem_cgroup_css_from_page() which returns the cgroup_subsys_state of the memcg associated with a given page. This will be used by cgroup writeback support. This function assumes that page->mem_cgroup association doesn't change until the page is released, which is true on the default hierarchy as long as replace_page_cache_page() is not used. As the only user of replace_page_cache_page() is FUSE which won't support cgroup writeback for the time being, this works for now, and replace_page_cache_page() will soon be updated so that the invariant actually holds. v3: s/mem_cgroup_migrate()/mem_cgroup_css_from_page()/ v2: Trigger WARN if the function is used on the traditional hierarchies and add comment about the assumed invariant. Signed-off-by: Tejun Heo Cc: Johannes Weiner Cc: Michal Hocko --- include/linux/memcontrol.h | 1 + mm/memcontrol.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 294498f..637ef62 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -115,6 +115,7 @@ static inline bool mm_match_cgroup(struct mm_struct *mm, } extern struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *memcg); +extern struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page); struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *, struct mem_cgroup *, diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b22a92b..c856cec 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -598,6 +598,37 @@ struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *memcg) return &memcg->css; } +/** + * mem_cgroup_css_from_page - css of the memcg associated with a page + * @page: page of interest + * + * This function is guaranteed to return a valid cgroup_subsys_state and + * the returned css remains associated with @page until it is released. + * + * This can only be used on the default hierarchy as @page's memcg + * association may change on the traditional hierarchies. Use + * try_get_mem_cgroup_from_page() instead on the traditional hierarchies. + * + * XXX: The above comment isn't true yet as replace_page_cache_page() can + * modify the association before @page is released even on the default + * hierarchy; however, the current and planned usages don't mix the + * the two functions and replace_page_cache_page() will soon be + * updated to make the invariant actually true. + */ +struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page) +{ + struct cgroup_subsys_state *css; + + if (page->mem_cgroup) + css = &page->mem_cgroup->css; + else + css = &root_mem_cgroup->css; + + WARN_ON_ONCE(!cgroup_on_dfl(css->cgroup)); + + return css; +} + static struct mem_cgroup_per_zone * mem_cgroup_page_zoneinfo(struct mem_cgroup *memcg, struct page *page) { -- 2.4.0