Re: [memcg BUG] unable to handle kernel NULL pointer derefence at 00000000

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 21 Oct 2008 15:21:07 +0800
Li Zefan <lizf@cn.fujitsu.com> wrote:
> dmesg is attached.
> 
Thanks....I think I caught some. (added Mel Gorman to CC:)

NODE_DATA(nid)->spanned_pages just means sum of zone->spanned_pages in node.

So, If there is a hole between zone, node->spanned_pages doesn't mean
length of node's memmap....(then, some hole can be skipped.)

OMG....Could you try this ? 

-Kame
==
NODE_DATA(nid)->node_spanned_pages doesn't means width of node's memory
but means sum of spanned_pages in all zones of node.

alloc_node_page_cgroup() misunderstand it. This patch tries to use
the same algorithm as alloc_node_mem_map() for allocating page_cgroup()
for node.

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

 mm/page_cgroup.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

Index: linux-2.6.27/mm/page_cgroup.c
===================================================================
--- linux-2.6.27.orig/mm/page_cgroup.c
+++ linux-2.6.27/mm/page_cgroup.c
@@ -41,10 +41,18 @@ static int __init alloc_node_page_cgroup
 {
 	struct page_cgroup *base, *pc;
 	unsigned long table_size;
-	unsigned long start_pfn, nr_pages, index;
+	unsigned long start, end, start_pfn, nr_pages, index;
 
-	start_pfn = NODE_DATA(nid)->node_start_pfn;
-	nr_pages = NODE_DATA(nid)->node_spanned_pages;
+	/*
+	 * Instead of allocating page_cgroup for [start, end)
+	 * We allocate page_cgroup to the same size of mem_map.
+	 * See page_alloc.c::alloc_node_mem_map()
+	 */
+	start = NODE_DATA(nid)->node_start_pfn & ~(MAX_ORDER_NR_PAGES - 1);
+	end = NODE_DATA(nid)->node_start_pfn
+			+ NODE_DATA(nid)->node_spanned_pages;
+	end = ALIGN(end, MAX_ORDER_NR_PAGES);
+	nr_pages = end - start;
 
 	table_size = sizeof(struct page_cgroup) * nr_pages;
 
@@ -52,6 +60,9 @@ static int __init alloc_node_page_cgroup
 			table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS));
 	if (!base)
 		return -ENOMEM;
+
+	start_pfn = NODE_DATA(nid)->node_start_pfn;
+	base = base + start_pfn - start;
 	for (index = 0; index < nr_pages; index++) {
 		pc = base + index;
 		__init_page_cgroup(pc, start_pfn + index);

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