Author: alc
Date: Sat Sep 3 03:14:24 2016
New Revision: 305319
URL: https://svnweb.freebsd.org/changeset/base/305319
Log:
As an optimization to the machine-independent layer, change the machine-
dependent pmap_ts_referenced() so that it updates 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() by the machine-
independent layer.
MFC after: 3 weeks
Modified:
head/sys/arm/arm/pmap-v6.c
Modified: head/sys/arm/arm/pmap-v6.c
==============================================================================
--- head/sys/arm/arm/pmap-v6.c Sat Sep 3 02:51:46 2016 (r305318)
+++ head/sys/arm/arm/pmap-v6.c Sat Sep 3 03:14:24 2016 (r305319)
@@ -5178,6 +5178,14 @@ pmap_is_referenced(vm_page_t m)
* 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)
@@ -5186,7 +5194,7 @@ pmap_ts_referenced(vm_page_t m)
pv_entry_t pv, pvf;
pmap_t pmap;
pt1_entry_t *pte1p, opte1;
- pt2_entry_t *pte2p;
+ pt2_entry_t *pte2p, opte2;
vm_paddr_t pa;
int rtval = 0;
@@ -5205,6 +5213,14 @@ pmap_ts_referenced(vm_page_t m)
PMAP_LOCK(pmap);
pte1p = pmap_pte1(pmap, pv->pv_va);
opte1 = pte1_load(pte1p);
+ if (pte1_is_dirty(opte1)) {
+ /*
+ * Although "opte1" is mapping a 1MB page, because
+ * this function is called at a 4KB page granularity,
+ * we only update the 4KB page under test.
+ */
+ vm_page_dirty(m);
+ }
if ((opte1 & PTE1_A) != 0) {
/*
* Since this reference bit is shared by 256 4KB pages,
@@ -5253,7 +5269,10 @@ small_mappings:
("%s: not found a link in page %p's pv list", __func__, m));
pte2p = pmap_pte2_quick(pmap, pv->pv_va);
- if ((pte2_load(pte2p) & PTE2_A) != 0) {
+ opte2 = pte2_load(pte2p);
+ if (pte2_is_dirty(opte2))
+ vm_page_dirty(m);
+ if ((opte2 & PTE2_A) != 0) {
pte2_clear_bit(pte2p, PTE2_A);
pmap_tlb_flush(pmap, pv->pv_va);
rtval++;
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