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

[Wu Fengguang <fengguang.wu@intel.com>]

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);

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