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mm: page_cgroup: check page_cgroup arrays in lookup_page_cgroup() only when necessary

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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>
This commit is contained in:
Johannes Weiner 2012-01-12 17:18:40 -08:00 committed by Linus Torvalds
parent cfa449461e
commit 00c54c0bac
1 changed files with 16 additions and 2 deletions
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18
mm/page_cgroup.c
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@ -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;
}