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Index: amd64/amd64/pmap.c
===================================================================
--- amd64/amd64/pmap.c
+++ amd64/amd64/pmap.c
@@ -5843,6 +5843,14 @@
* 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 all
+ * dirty pages. Some dirty pages will only be detected by a future call
+ * to pmap_is_modified().
+ *
* A DI block is not needed within this function, because
* invalidations are performed before the PV list lock is
* released.
@@ -5855,7 +5863,7 @@
pmap_t pmap;
struct rwlock *lock;
pd_entry_t oldpde, *pde;
- pt_entry_t *pte, PG_A;
+ pt_entry_t *pte, PG_A, PG_M, PG_RW;
vm_offset_t va;
vm_paddr_t pa;
int cleared, md_gen, not_cleared, pvh_gen;
@@ -5890,9 +5898,19 @@
}
}
PG_A = pmap_accessed_bit(pmap);
+ PG_M = pmap_modified_bit(pmap);
+ PG_RW = pmap_rw_bit(pmap);
va = pv->pv_va;
pde = pmap_pde(pmap, pv->pv_va);
oldpde = *pde;
+ if ((oldpde & (PG_M | PG_RW)) == (PG_M | PG_RW)) {
+ /*
+ * Although "oldpde" 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 ((*pde & PG_A) != 0) {
/*
* Since this reference bit is shared by 512 4KB
@@ -5986,11 +6004,15 @@
}
}
PG_A = pmap_accessed_bit(pmap);
+ PG_M = pmap_modified_bit(pmap);
+ PG_RW = pmap_rw_bit(pmap);
pde = pmap_pde(pmap, pv->pv_va);
KASSERT((*pde & PG_PS) == 0,
("pmap_ts_referenced: found a 2mpage in page %p's pv list",
m));
pte = pmap_pde_to_pte(pde, pv->pv_va);
+ if ((*pte & (PG_M | PG_RW)) == (PG_M | PG_RW))
+ vm_page_dirty(m);
if ((*pte & PG_A) != 0) {
if (safe_to_clear_referenced(pmap, *pte)) {
atomic_clear_long(pte, PG_A);
Index: vm/vm_pageout.c
===================================================================
--- vm/vm_pageout.c
+++ vm/vm_pageout.c
@@ -839,6 +839,11 @@
return (error);
}
+int counter_yes;
+SYSCTL_INT(_debug, OID_AUTO, counter_yes, CTLFLAG_RD, &counter_yes, 0, "");
+int counter_no;
+SYSCTL_INT(_debug, OID_AUTO, counter_no, CTLFLAG_RD, &counter_no, 0, "");
+
/*
* vm_pageout_scan does the dirty work for the pageout daemon.
*
@@ -1016,7 +1021,12 @@
} else
act_delta = 0;
if (object->ref_count != 0) {
+ bool flag = m->dirty == 0;
act_delta += pmap_ts_referenced(m);
+ if (flag && m->dirty != 0)
+ counter_yes++;
+ else
+ counter_no++;
} else {
KASSERT(!pmap_page_is_mapped(m),
("vm_pageout_scan: page %p is mapped", m));

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