Re: [PATCH] [11/16] HWPOISON: check and isolate corrupted free pages v2

Nick Piggin
2009-06-09T10:02:35Z

On Wed, Jun 03, 2009 at 08:46:45PM +0200, Andi Kleen wrote:
>
> From: Wu Fengguang <fengguang.wu@intel.com>
>
> If memory corruption hits the free buddy pages, we can safely ignore them.
> No one will access them until page allocation time, then prep_new_page()
> will automatically check and isolate PG_hwpoison page for us (for 0-order
> allocation).

It would be kinda nice if this could be done in the handler
directly (ie. take the page directly out of the allocator
or pcp list). Completely avoiding fastpaths would be a
wonderful goal.

>
> This patch expands prep_new_page() to check every component page in a high
> order page allocation, in order to completely stop PG_hwpoison pages from
> being recirculated.
>
> Note that the common case -- only allocating a single page, doesn't
> do any more work than before. Allocating > order 0 does a bit more work,
> but that's relatively uncommon.
>
> This simple implementation may drop some innocent neighbor pages, hopefully
> it is not a big problem because the event should be rare enough.
>
> This patch adds some runtime costs to high order page users.
>
> [AK: Improved description]
>
> v2: Andi Kleen:
> Port to -mm code
> Move check into separate function.
> Don't dump stack in bad_pages for hwpoisoned pages.
> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
>
> ---
> mm/page_alloc.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> Index: linux/mm/page_alloc.c
> ===================================================================
> --- linux.orig/mm/page_alloc.c 2009-06-03 19:37:39.000000000 +0200
> +++ linux/mm/page_alloc.c 2009-06-03 20:13:43.000000000 +0200
> @@ -237,6 +237,12 @@
> static unsigned long nr_shown;
> static unsigned long nr_unshown;
>
> + /* Don't complain about poisoned pages */
> + if (PageHWPoison(page)) {
> + __ClearPageBuddy(page);
> + return;
> + }
> +
> /*
> * Allow a burst of 60 reports, then keep quiet for that minute;
> * or allow a steady drip of one report per second.
> @@ -650,7 +656,7 @@
> /*
> * This page is about to be returned from the page allocator
> */
> -static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
> +static inline int check_new_page(struct page *page)
> {
> if (unlikely(page_mapcount(page) |
> (page->mapping != NULL) |
> @@ -659,6 +665,18 @@
> bad_page(page);
> return 1;
> }
> + return 0;
> +}
> +
> +static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
> +{
> + int i;
> +
> + for (i = 0; i < (1 << order); i++) {
> + struct page *p = page + i;
> + if (unlikely(check_new_page(p)))
> + return 1;
> + }
>
> set_page_private(page, 0);
> set_page_refcounted(page);