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@xxxxxxxxxxx>
---
mm/page_cgroup.c | 18 ++++++++++++++++--
1 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index a14655d..58405ca 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;
}
@@ -87,9 +94,16 @@ 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;
}
--
1.7.6.4
--
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