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From: Alan Cox <alc@FreeBSD.org>
Date: Sat, 6 Oct 2012 19:05:50 +0000 (UTC)
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Subject: svn commit: r241276 - head/sys/mips/mips
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Author: alc
Date: Sat Oct  6 19:05:50 2012
New Revision: 241276
URL: http://svn.freebsd.org/changeset/base/241276

Log:
  Correct two pessimizations in pmap_extract_and_hold().  Test the PTE for
  having PTE_RO set instead of PTE_D.  This avoids some unnecessary failures
  by pmap_extract_and_hold() that will have to be handled by a call to
  vm_fault_hold().  Testing the PTE for both being non-zero and having PTE_V
  set is redundant.  The latter suffices.

Modified:
  head/sys/mips/mips/pmap.c

Modified: head/sys/mips/mips/pmap.c
==============================================================================
--- head/sys/mips/mips/pmap.c	Sat Oct  6 19:01:31 2012	(r241275)
+++ head/sys/mips/mips/pmap.c	Sat Oct  6 19:05:50 2012	(r241276)
@@ -791,24 +791,25 @@ pmap_extract(pmap_t pmap, vm_offset_t va
 vm_page_t
 pmap_extract_and_hold(pmap_t pmap, vm_offset_t va, vm_prot_t prot)
 {
-	pt_entry_t *ptep;
-	pt_entry_t pte;
+	pt_entry_t pte, *ptep;
+	vm_paddr_t pa, pte_pa;
 	vm_page_t m;
-	vm_paddr_t pa;
 
 	m = NULL;
 	pa = 0;
 	PMAP_LOCK(pmap);
 retry:
 	ptep = pmap_pte(pmap, va);
-	if ((ptep != NULL)  && ((pte = *ptep) != 0) && 
-	    pte_test(&pte, PTE_V) &&
-	    (pte_test(&pte, PTE_D) || (prot & VM_PROT_WRITE) == 0)) {
-		if (vm_page_pa_tryrelock(pmap, TLBLO_PTE_TO_PA(pte), &pa))
-			goto retry;
-
-		m = PHYS_TO_VM_PAGE(TLBLO_PTE_TO_PA(pte));
-		vm_page_hold(m);
+	if (ptep != NULL) {
+		pte = *ptep;
+		if (pte_test(&pte, PTE_V) && (!pte_test(&pte, PTE_RO) ||
+		    (prot & VM_PROT_WRITE) == 0)) {
+			pte_pa = TLBLO_PTE_TO_PA(pte);
+			if (vm_page_pa_tryrelock(pmap, pte_pa, &pa))
+				goto retry;
+			m = PHYS_TO_VM_PAGE(pte_pa);
+			vm_page_hold(m);
+		}
 	}
 	PA_UNLOCK_COND(pa);
 	PMAP_UNLOCK(pmap);