Messages in this thread Patch in this message | | | From | Mel Gorman <> | Subject | [PATCH 01/46] x86: mm: only do a local tlb flush in ptep_set_access_flags() | Date | Wed, 21 Nov 2012 10:21:07 +0000 |
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From: Rik van Riel <riel@redhat.com>
The function ptep_set_access_flags() is only ever invoked to set access flags or add write permission on a PTE. The write bit is only ever set together with the dirty bit.
Because we only ever upgrade a PTE, it is safe to skip flushing entries on remote TLBs. The worst that can happen is a spurious page fault on other CPUs, which would flush that TLB entry.
Lazily letting another CPU incur a spurious page fault occasionally is (much!) cheaper than aggressively flushing everybody else's TLB.
Signed-off-by: Rik van Riel <riel@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Michel Lespinasse <walken@google.com> Cc: Ingo Molnar <mingo@kernel.org> --- arch/x86/mm/pgtable.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 8573b83..be3bb46 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -301,6 +301,13 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd) free_page((unsigned long)pgd); } +/* + * Used to set accessed or dirty bits in the page table entries + * on other architectures. On x86, the accessed and dirty bits + * are tracked by hardware. However, do_wp_page calls this function + * to also make the pte writeable at the same time the dirty bit is + * set. In that case we do actually need to write the PTE. + */ int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address, pte_t *ptep, pte_t entry, int dirty) @@ -310,7 +317,7 @@ int ptep_set_access_flags(struct vm_area_struct *vma, if (changed && dirty) { *ptep = entry; pte_update_defer(vma->vm_mm, address, ptep); - flush_tlb_page(vma, address); + __flush_tlb_one(address); } return changed; -- 1.7.9.2
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