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    SubjectRe: [PATCH 10/22] HWPOISON: check and isolate corrupted free pages v2
    On Mon, 15 Jun 2009 18:16:20 +0800
    Wu Fengguang <fengguang.wu@intel.com> wrote:

    > On Mon, Jun 15, 2009 at 05:41:12PM +0800, KAMEZAWA Hiroyuki wrote:
    > > On Mon, 15 Jun 2009 10:45:30 +0800
    > > Wu Fengguang <fengguang.wu@intel.com> 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).
    > > >
    > > > 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(-)
    > > >
    > > > --- sound-2.6.orig/mm/page_alloc.c
    > > > +++ sound-2.6/mm/page_alloc.c
    > > > @@ -233,6 +233,12 @@ static void bad_page(struct page *page)
    > > > static unsigned long nr_shown;
    > > > static unsigned long nr_unshown;
    > > >
    > > > + /* Don't complain about poisoned pages */
    > > > + if (PageHWPoison(page)) {
    > > > + __ClearPageBuddy(page);
    > > > + return;
    > > > + }
    > >
    > > Hmm ? why __ClearPageBuddy() is necessary ?
    >
    > Because this page is considered to be "allocated" out of the buddy
    > system, even though we fail the allocation here.
    >
    > The page is now owned by no one, especially not owned by the buddy
    > allocator.
    >
    I just wonder "why __ClearPageBuddy() is necessary."

    When bad_page() is called, a page is removed from buddy allocator and no
    PG_buddy flag at all....I'm sorry if you added bad_page() caller in buddy allocator.

    Buddy Allocator I call here is just 2 functions.
    - __free_one_page()
    - expand()


    Bye,
    -Kame



    > Thanks,
    > Fengguang
    >



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