Messages in this thread |  | | | Subject | Re: [PATCH 3/3] Guarantee that COW faults for a process that called mmap(MAP_PRIVATE) on hugetlbfs will succeed | | From | Adam Litke <> | | Date | Wed, 14 May 2008 15:55:25 -0500 |
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On Wed, 2008-05-07 at 20:39 +0100, Mel Gorman wrote:
> diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.25-mm1-0020-map_private_reserve/mm/hugetlb.c linux-2.6.25-mm1-0030-reliable_parent_faults/mm/hugetlb.c > --- linux-2.6.25-mm1-0020-map_private_reserve/mm/hugetlb.c 2008-05-07 18:39:34.000000000 +0100 > +++ linux-2.6.25-mm1-0030-reliable_parent_faults/mm/hugetlb.c 2008-05-07 20:05:18.000000000 +0100 > @@ -40,6 +40,9 @@ static int hugetlb_next_nid; > */ > static DEFINE_SPINLOCK(hugetlb_lock); > > +#define HPAGE_RESV_OWNER (1UL << (BITS_PER_LONG - 1)) > +#define HPAGE_RESV_UNMAPPED (1UL << (BITS_PER_LONG - 2)) > +#define HPAGE_RESV_MASK (HPAGE_RESV_OWNER | HPAGE_RESV_UNMAPPED) > /* > * These three helpers are used to track how many pages are reserved for > * faults in a MAP_PRIVATE mapping. Only the process that called mmap() > @@ -49,20 +52,23 @@ static unsigned long vma_resv_huge_pages > { > VM_BUG_ON(!is_vm_hugetlb_page(vma)); > if (!(vma->vm_flags & VM_SHARED)) > - return (unsigned long)vma->vm_private_data; > + return (unsigned long)vma->vm_private_data & ~HPAGE_RESV_MASK; > return 0; > }
Ick. Though I don't really have a suggestion on how to improve it unless a half-word is enough room to contain the reservation. In that case we could create a structure which would make this much clearer.
struct hugetlb_vma_reservation { unsigned int flags; unsigned int resv; }; > static void adjust_vma_resv_huge_pages(struct vm_area_struct *vma, int delta) > { > unsigned long reserve; > + unsigned long flags; > VM_BUG_ON(vma->vm_flags & VM_SHARED); > VM_BUG_ON(!is_vm_hugetlb_page(vma)); > > reserve = (unsigned long)vma->vm_private_data + delta; > - vma->vm_private_data = (void *)reserve; > + flags = (unsigned long)vma->vm_private_data & HPAGE_RESV_MASK; > + vma->vm_private_data = (void *)(reserve | flags); > } > > +/* Reset counters to 0 and clear all HPAGE_RESV_* flags */ > void reset_vma_resv_huge_pages(struct vm_area_struct *vma) > { > VM_BUG_ON(!is_vm_hugetlb_page(vma)); > @@ -73,10 +79,27 @@ void reset_vma_resv_huge_pages(struct vm > static void set_vma_resv_huge_pages(struct vm_area_struct *vma, > unsigned long reserve) > { > + unsigned long flags; > + > VM_BUG_ON(!is_vm_hugetlb_page(vma)); > VM_BUG_ON(vma->vm_flags & VM_SHARED); > > - vma->vm_private_data = (void *)reserve; > + flags = (unsigned long)vma->vm_private_data & HPAGE_RESV_MASK; > + vma->vm_private_data = (void *)(reserve | flags); > +} > + > +static void set_vma_resv_flags(struct vm_area_struct *vma, unsigned long flags) > +{ > + unsigned long reserveflags = (unsigned long)vma->vm_private_data; > + VM_BUG_ON(!is_vm_hugetlb_page(vma)); > + reserveflags |= flags; > + vma->vm_private_data = (void *)reserveflags; > +} > + > +static int is_vma_resv_set(struct vm_area_struct *vma, unsigned long flag) > +{ > + VM_BUG_ON(!is_vm_hugetlb_page(vma)); > + return ((unsigned long)vma->vm_private_data & flag) != 0; > } > > static void clear_huge_page(struct page *page, unsigned long addr) > @@ -139,7 +162,7 @@ static void decrement_hugepage_resv_vma( > * Only the process that called mmap() has reserves for > * private mappings. > */ > - if (vma_resv_huge_pages(vma)) { > + if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) { > resv_huge_pages--; > adjust_vma_resv_huge_pages(vma, -1); > }
-- Adam Litke - (agl at us.ibm.com) IBM Linux Technology Center
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