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Index: head/sys/amd64/amd64/pmap.c
===================================================================
--- head/sys/amd64/amd64/pmap.c
+++ head/sys/amd64/amd64/pmap.c
@@ -5816,8 +5816,6 @@
return (FALSE);
}
-#define PMAP_TS_REFERENCED_MAX 5
-
/*
* pmap_ts_referenced:
*
@@ -5826,10 +5824,6 @@
* 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
@@ -5898,7 +5892,7 @@
*/
vm_page_dirty(m);
}
- if ((*pde & PG_A) != 0) {
+ if ((oldpde & PG_A) != 0) {
/*
* Since this reference bit is shared by 512 4KB
* pages, it should not be cleared every time it is
@@ -5919,7 +5913,7 @@
*/
if ((((pa >> PAGE_SHIFT) ^ (pv->pv_va >> PDRSHIFT) ^
(uintptr_t)pmap) & (NPTEPG - 1)) == 0 &&
- (*pde & PG_W) == 0) {
+ (oldpde & PG_W) == 0) {
if (safe_to_clear_referenced(pmap, oldpde)) {
atomic_clear_long(pde, PG_A);
pmap_invalidate_page(pmap, pv->pv_va);
Index: head/sys/arm/arm/pmap-v6.c
===================================================================
--- head/sys/arm/arm/pmap-v6.c
+++ head/sys/arm/arm/pmap-v6.c
@@ -5161,8 +5161,6 @@
return (rv);
}
-#define PMAP_TS_REFERENCED_MAX 5
-
/*
* pmap_ts_referenced:
*
@@ -5171,10 +5169,6 @@
* 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
Index: head/sys/arm64/arm64/pmap.c
===================================================================
--- head/sys/arm64/arm64/pmap.c
+++ head/sys/arm64/arm64/pmap.c
@@ -3880,8 +3880,6 @@
return (FALSE);
}
-#define PMAP_TS_REFERENCED_MAX 5
-
/*
* pmap_ts_referenced:
*
@@ -3890,9 +3888,13 @@
* 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().
*/
int
pmap_ts_referenced(vm_page_t m)
@@ -3947,6 +3949,14 @@
("pmap_ts_referenced: found an invalid l1 table"));
pte = pmap_l1_to_l2(pde, pv->pv_va);
tpte = pmap_load(pte);
+ if (pmap_page_dirty(tpte)) {
+ /*
+ * Although "tpte" is mapping a 2MB page, because
+ * this function is called at a 4KB page granularity,
+ * we only update the 4KB page under test.
+ */
+ vm_page_dirty(m);
+ }
if ((tpte & ATTR_AF) != 0) {
/*
* Since this reference bit is shared by 512 4KB
@@ -4043,6 +4053,8 @@
("pmap_ts_referenced: found an invalid l2 table"));
pte = pmap_l2_to_l3(pde, pv->pv_va);
tpte = pmap_load(pte);
+ if (pmap_page_dirty(tpte))
+ vm_page_dirty(m);
if ((tpte & ATTR_AF) != 0) {
if (safe_to_clear_referenced(pmap, tpte)) {
/*
Index: head/sys/i386/i386/pmap.c
===================================================================
--- head/sys/i386/i386/pmap.c
+++ head/sys/i386/i386/pmap.c
@@ -4765,8 +4765,6 @@
rw_wunlock(&pvh_global_lock);
}
-#define PMAP_TS_REFERENCED_MAX 5
-
/*
* pmap_ts_referenced:
*
@@ -4775,10 +4773,6 @@
* 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
Index: head/sys/powerpc/booke/pmap.c
===================================================================
--- head/sys/powerpc/booke/pmap.c
+++ head/sys/powerpc/booke/pmap.c
@@ -2499,9 +2499,13 @@
* 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)
@@ -2518,6 +2522,8 @@
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();
@@ -2528,7 +2534,7 @@
tlb_miss_unlock();
mtx_unlock_spin(&tlbivax_mutex);
- if (++count > 4) {
+ if (++count >= PMAP_TS_REFERENCED_MAX) {
PMAP_UNLOCK(pv->pv_pmap);
break;
}
Index: head/sys/riscv/riscv/pmap.c
===================================================================
--- head/sys/riscv/riscv/pmap.c
+++ head/sys/riscv/riscv/pmap.c
@@ -2991,8 +2991,6 @@
return (FALSE);
}
-#define PMAP_TS_REFERENCED_MAX 5
-
/*
* pmap_ts_referenced:
*
@@ -3001,9 +2999,13 @@
* 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().
*/
int
pmap_ts_referenced(vm_page_t m)
@@ -3012,7 +3014,7 @@
pmap_t pmap;
struct rwlock *lock;
pd_entry_t *l2;
- pt_entry_t *l3;
+ pt_entry_t *l3, old_l3;
vm_paddr_t pa;
int cleared, md_gen, not_cleared;
struct spglist free;
@@ -3050,15 +3052,18 @@
("pmap_ts_referenced: found an invalid l2 table"));
l3 = pmap_l2_to_l3(l2, pv->pv_va);
- if ((pmap_load(l3) & PTE_A) != 0) {
- if (safe_to_clear_referenced(pmap, pmap_load(l3))) {
+ old_l3 = pmap_load(l3);
+ if (pmap_page_dirty(old_l3))
+ vm_page_dirty(m);
+ if ((old_l3 & PTE_A) != 0) {
+ if (safe_to_clear_referenced(pmap, old_l3)) {
/*
* TODO: We don't handle the access flag
* at all. We need to be able to set it in
* the exception handler.
*/
panic("RISCVTODO: safe_to_clear_referenced\n");
- } else if ((pmap_load(l3) & PTE_SW_WIRED) == 0) {
+ } else if ((old_l3 & PTE_SW_WIRED) == 0) {
/*
* Wired pages cannot be paged out so
* doing accessed bit emulation for
Index: head/sys/sparc64/sparc64/pmap.c
===================================================================
--- head/sys/sparc64/sparc64/pmap.c
+++ head/sys/sparc64/sparc64/pmap.c
@@ -2073,18 +2073,12 @@
return (rv);
}
-#define PMAP_TS_REFERENCED_MAX 5
-
/*
* Return a count of reference bits for a page, clearing those bits.
* It is not necessary for every reference bit to be cleared, but it
* 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
Index: head/sys/vm/pmap.h
===================================================================
--- head/sys/vm/pmap.h
+++ head/sys/vm/pmap.h
@@ -104,6 +104,16 @@
#define PMAP_ENTER_NOSLEEP 0x0100
#define PMAP_ENTER_WIRED 0x0200
+/*
+ * Define the maximum number of machine-dependent reference bits that are
+ * cleared by a call to pmap_ts_referenced(). This limit serves two purposes.
+ * First, it bounds the cost of reference bit maintenance on widely shared
+ * pages. Second, it prevents numeric overflow during maintenance of a
+ * widely shared page's "act_count" field. An overflow could result in the
+ * premature deactivation of the page.
+ */
+#define PMAP_TS_REFERENCED_MAX 5
+
void pmap_activate(struct thread *td);
void pmap_advise(pmap_t pmap, vm_offset_t sva, vm_offset_t eva,
int advice);

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