mm: page_cgroup: check page_cgroup arrays in lookup_page_cgroup() only when necessary (00c54c0b) · Commits · 戴 / test

lookup_page_cgroup() is usually used only against pages that are used in userspace. The exception is the CONFIG_DEBUG_VM-only memcg check from the page allocator: it can run on pages without page_cgroup descriptors allocated when the pages are fed into the page allocator for the first time during boot or memory hotplug. Include the array check only when CONFIG_DEBUG_VM is set and save the unnecessary check in production kernels. Signed-off-by:

Johannes Weiner <hannes@cmpxchg.org> Acked-by:

KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by:

Michal Hocko <mhocko@suse.cz> Cc: Balbir Singh <bsingharora@gmail.com> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/page_cgroup.c

+16 −2

Original line number	Diff line number	Diff line
		@@ -28,9 +28,16 @@ struct page_cgroup lookup_page_cgroup(struct page page)
		struct page_cgroup *base;

		base = NODE_DATA(page_to_nid(page))->node_page_cgroup;
		#ifdef CONFIG_DEBUG_VM
		/*
		* The sanity checks the page allocator does upon freeing a
		* page can reach here before the page_cgroup arrays are
		* allocated when feeding a range of pages to the allocator
		* for the first time during bootup or memory hotplug.
		*/
		if (unlikely(!base))
		return NULL;

		#endif
		offset = pfn - NODE_DATA(page_to_nid(page))->node_start_pfn;
		return base + offset;
		}
		@@ -85,9 +92,16 @@ struct page_cgroup lookup_page_cgroup(struct page page)
		{
		unsigned long pfn = page_to_pfn(page);
		struct mem_section *section = __pfn_to_section(pfn);

		#ifdef CONFIG_DEBUG_VM
		/*
		* The sanity checks the page allocator does upon freeing a
		* page can reach here before the page_cgroup arrays are
		* allocated when feeding a range of pages to the allocator
		* for the first time during bootup or memory hotplug.
		*/
		if (!section->page_cgroup)
		return NULL;
		#endif
		return section->page_cgroup + pfn;
		}

Admin message