From 00c54c0bac24bb02d2460c516da76651a7451286 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Thu, 12 Jan 2012 17:18:40 -0800 Subject: 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: Johannes Weiner Acked-by: KAMEZAWA Hiroyuki Acked-by: Michal Hocko Cc: Balbir Singh Cc: David Rientjes Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_cgroup.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) (limited to 'mm') diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c index f0559e049e0..e910524e5a0 100644 --- a/mm/page_cgroup.c +++ b/mm/page_cgroup.c @@ -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; } -- cgit v1.2.3