Commit 0f9a921c authored Nov 06, 2012 by Rik van Riel Committed by Mel Gorman Dec 11, 2012

x86: mm: only do a local tlb flush in ptep_set_access_flags()



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>

parent f4a75d2e

arch/x86/mm/pgtable.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -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;