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As an optimization to the machine-independent layer, change the machine-

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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
This commit is contained in:
Alan Cox 2016-09-03 03:14:24 +00:00
parent 6e988609cf
commit d0881641d4
1 changed files with 21 additions and 2 deletions
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23
sys/arm/arm/pmap-v6.c
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@ -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 @@ pmap_ts_referenced(vm_page_t m)
("%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++;