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

Wu Fengguang
2009-06-09T13:03:19Z

On Tue, Jun 09, 2009 at 06:02:29PM +0800, Nick Piggin wrote:
> 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.

In fact Andi have code to do that. We prefer this one because
- it's simple
- it's good sanity check for possible software BUGs
- it mainly adds overhead to high order pages, which is acceptable

Thanks,
Fengguang

> >
> > + /* Don't complain about poisoned pages */
> > + if (PageHWPoison(page)) {
> > + __ClearPageBuddy(page);
> > + return;
> > + }
> > +

I do think the above chunk is not absolutely necessary, though.

Thanks,
Fengguang

> > /*
> > * 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);