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Commit 00c54c0b authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds
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mm: page_cgroup: check page_cgroup arrays in lookup_page_cgroup() only when necessary 



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: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarMichal 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cfa44946

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;

}