MFC r305685

  Various changes to pmap_ts_referenced()

  Move PMAP_TS_REFERENCED_MAX out of the various pmap implementations and
  into vm/pmap.h, and describe what its purpose is.  Eliminate the archaic
  "XXX" comment about its value.  I don't believe that its exact value, e.g.,
  5 versus 6, matters.

  Update the arm64 and riscv pmap implementations of pmap_ts_referenced()
  to opportunistically update the page's dirty field.

  On amd64, use the PDE value already cached in a local variable rather than
  dereferencing a pointer again and again.

1 files changed, 10 insertions, 4 deletions

diff --git a/sys/powerpc/booke/pmap.c b/sys/powerpc/booke/pmap.c
index b7ffdd6..0448129 100644
--- a/sys/powerpc/booke/pmap.c
+++ b/sys/powerpc/booke/pmap.c
@@ -2527,9 +2527,13 @@ mmu_booke_clear_modify(mmu_t mmu, vm_page_t m)
  * is necessary that 0 only be returned when there are truly no
  * reference bits set.
  *
- * XXX: The exact number of bits to check and clear is a matter that
- * should be tested and standardized at some point in the future for
- * optimal aging of shared pages.
+ * As an optimization, update the page's dirty field if a modified bit is
+ * found while counting reference bits.  This opportunistic update can be
+ * performed at low cost and can eliminate the need for some future calls
+ * to pmap_is_modified().  However, since this function stops after
+ * finding PMAP_TS_REFERENCED_MAX reference bits, it may not detect some
+ * dirty pages.  Those dirty pages will only be detected by a future call
+ * to pmap_is_modified().
  */
 static int
 mmu_booke_ts_referenced(mmu_t mmu, vm_page_t m)
@@ -2546,6 +2550,8 @@ mmu_booke_ts_referenced(mmu_t mmu, vm_page_t m)
 		PMAP_LOCK(pv->pv_pmap);
 		if ((pte = pte_find(mmu, pv->pv_pmap, pv->pv_va)) != NULL &&
 		    PTE_ISVALID(pte)) {
+			if (PTE_ISMODIFIED(pte))
+				vm_page_dirty(m);
 			if (PTE_ISREFERENCED(pte)) {
 				mtx_lock_spin(&tlbivax_mutex);
 				tlb_miss_lock();
@@ -2556,7 +2562,7 @@ mmu_booke_ts_referenced(mmu_t mmu, vm_page_t m)
 				tlb_miss_unlock();
 				mtx_unlock_spin(&tlbivax_mutex);
 
-				if (++count > 4) {
+				if (++count >= PMAP_TS_REFERENCED_MAX) {
 					PMAP_UNLOCK(pv->pv_pmap);
 					break;
 				}