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    SubjectRe: [PATCH] [11/16] HWPOISON: check and isolate corrupted free pages v2
    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);


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