On Mon, Nov 26, 2012 at 07:06:53AM -0800, Dave Hansen wrote:
> On 11/26/2012 03:23 AM, Mel Gorman wrote:
> > On Wed, Nov 21, 2012 at 02:21:51PM -0500, Dave Hansen wrote:
> >>
> >> This needs to make it in before 3.7 is released.
> >>
> >
> > This is also required. Dave, can you double check? The surprise is that
> > this does not blow up very obviously.
> ...
> > @@ -1422,7 +1422,7 @@ int capture_free_page(struct page *page, int alloc_order, int migratetype)
> > }
> > }
> >
> > - return 1UL << order;
> > + return 1UL << alloc_order;
> > }
>
> compact_capture_page() only looks at the boolean return value out of
> capture_free_page(), so it wouldn't notice. split_free_page() does.
> But, when it calls capture_free_page(), order==alloc_order, so it
> wouldn't make a difference. So, there's probably no actual bug here,
> but it's certainly a wrong return value.
>
I don't think it is fine in this case.
isolate_freepages_block
isolated = split_free_page(page);
-> split_free_page
nr_pages = capture_free_page(page, order, 0);
-> capture_free_page (returns wrong value of too many pages)
return nr_pages;
so now isolate_freepages_block has the wrong value with nr_pages holding
a value for a larger number of pages than are really isolated and does
this
for (i = 0; i < isolated; i++) {
list_add(&page->lru, freelist);
page++;
}
so potentially that is now adding pages that are already on the buddy list
to the local free list and "fun" ensues.
--
Mel Gorman
SUSE Labs
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