Messages in this thread | | | Date | Tue, 9 Jun 2009 15:28:47 +0200 | From | Nick Piggin <> | Subject | Re: [PATCH] [11/16] HWPOISON: check and isolate corrupted free pages v2 |
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On Tue, Jun 09, 2009 at 09:03:04PM +0800, Wu Fengguang wrote: > 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
Yeah it's not bad. But we don't have much other non-debug options that check for random memory corruption like this. Given that the struct page is a very tiny proportion of memory, then I'm not totally convinced that all this checking in the page allocator is worthwhile for everyone. It's a much bigger cost if checks and branches have to be there just for hwpoison.
And I don't think removing a free page from the page allocator is too much more complex than removing a live page from the pagecache ;)
> > 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);
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