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SubjectRe: [PATCH] memcgroup: check and initialize page->cgroup in memmap_init_zone
On Fri, 18 Apr 2008 10:46:30 +0800 Shi Weihua <shiwh@cn.fujitsu.com> wrote:

> When we test memory controller in Fujitsu PrimeQuest(arch: ia64),
> the compiled kernel boots failed, the following message occured on
> the telnet terminal.
> -------------------------------------
> ..........
> ELILO boot: Uncompressing Linux... done
> Loading file initrd-2.6.25-rc9-00067-gb87e81e.img...done
> _ (system freezed)
> -------------------------------------
>
> We found commit 9442ec9df40d952b0de185ae5638a74970388e01
> causes this boot failure by git-bisect.
> And, we found the following change caused the boot failure.
> -------------------------------------
> @@ -2528,7 +2535,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zon
> set_page_links(page, zone, nid, pfn);
> init_page_count(page);
> reset_page_mapcount(page);
> - page_assign_page_cgroup(page, NULL);
> SetPageReserved(page);
>
> /*
> -------------------------------------
> In this patch, the Author Hugh Dickins said
> "...memmap_init_zone doesn't need it either, ...
> Linux assumes pointers in zeroed structures are NULL pointers."
> But it seems it's not always the case, so we should check and initialize
> page->cgroup anyways.
>
> Signed-off-by: Shi Weihua <shiwh@cn.fujitsu.com>
> ---
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 402a504..506d4cf 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2518,6 +2518,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> struct page *page;
> unsigned long end_pfn = start_pfn + size;
> unsigned long pfn;
> + void *pc;
>
> for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> /*
> @@ -2535,6 +2536,9 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> set_page_links(page, zone, nid, pfn);
> init_page_count(page);
> reset_page_mapcount(page);
> + pc = page_get_page_cgroup(page);
> + if (pc)
> + page_reset_bad_cgroup(page);
> SetPageReserved(page);
>

hm, fishy. Perhaps the architecture isn't zeroing the memmap arrays?

Or perhaps that page was used and then later freed before we got to
memmap_init_zone() and was freed with a non-zero ->page_cgroup. Which is
unlikely given that page.page_cgroup was only just added and is only
present if CONFIG_CGROUP_MEM_RES_CTLR.


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