Messages in this thread | | | Date | Fri, 11 Jul 2008 09:16:13 +0100 | From | Andy Whitcroft <> | Subject | Re: [PATCH 1/2] [PATCH] Fix a hugepage reservation check for MAP_SHARED |
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On Thu, Jul 10, 2008 at 06:30:21PM +0100, Mel Gorman wrote: > > When removing a huge page from the hugepage pool for a fault the system > checks to see if the mapping requires additional pages to be reserved, and > if it does whether there are any unreserved pages remaining. If not, the > allocation fails without even attempting to get a page. In order to determine > whether to apply this check we call vma_has_private_reserves() which tells us > if this vma is MAP_PRIVATE and is the owner. This incorrectly triggers the > remaining reservation test for MAP_SHARED mappings which prevents allocation > of the final page in the pool even though it is reserved for this mapping. > > In reality we only want to check this for MAP_PRIVATE mappings where the > process is not the original mapper. Replace vma_has_private_reserves() with > vma_has_reserves() which indicates whether further reserves are required, > and update the caller.
Acked-by: Andy Whitcroft <apw@shadowen.org>
> Signed-off-by: Mel Gorman <mel@csn.ul.ie> > --- > > mm/hugetlb.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.26-rc8-mm1-clean/mm/hugetlb.c linux-2.6.26-rc8-mm1-fix-needsreserve-check/mm/hugetlb.c > --- linux-2.6.26-rc8-mm1-clean/mm/hugetlb.c 2008-07-08 11:54:34.000000000 -0700 > +++ linux-2.6.26-rc8-mm1-fix-needsreserve-check/mm/hugetlb.c 2008-07-08 12:41:36.000000000 -0700 > @@ -343,13 +343,13 @@ void reset_vma_resv_huge_pages(struct vm > } > > /* Returns true if the VMA has associated reserve pages */ > -static int vma_has_private_reserves(struct vm_area_struct *vma) > +static int vma_has_reserves(struct vm_area_struct *vma) > { > if (vma->vm_flags & VM_SHARED) > - return 0; > - if (!is_vma_resv_set(vma, HPAGE_RESV_OWNER)) > - return 0; > - return 1; > + return 1; > + if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) > + return 1; > + return 0; > } > > static void clear_huge_page(struct page *page, > @@ -421,7 +421,7 @@ static struct page *dequeue_huge_page_vm > * have no page reserves. This check ensures that reservations are > * not "stolen". The child may still get SIGKILLed > */ > - if (!vma_has_private_reserves(vma) && > + if (!vma_has_reserves(vma) && > h->free_huge_pages - h->resv_huge_pages == 0) > return NULL; >
-apw
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