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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.

Reviewed by:	kib, markj
MFC after:	3 weeks
Sponsored by:	EMC / Isilon Storage Division
Differential Revision:	https://reviews.freebsd.org/D7722
This commit is contained in:
Alan Cox 2016-09-01 15:57:44 +00:00
parent 4c22fda976
commit 53aadae680
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=305213
2 changed files with 41 additions and 1 deletions
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24
sys/amd64/amd64/pmap.c
View File

@ -5843,6 +5843,14 @@ safe_to_clear_referenced(pmap_t pmap, pt_entry_t pte)
* 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().
*
* 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_ts_referenced(vm_page_t m)
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 @@ pmap_ts_referenced(vm_page_t m)
}
}
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 @@ pmap_ts_referenced(vm_page_t m)
}
}
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);

18
sys/i386/i386/pmap.c
View File

@ -4798,6 +4798,14 @@ pmap_remove_write(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)
@ -4824,6 +4832,14 @@ pmap_ts_referenced(vm_page_t m)
pmap = PV_PMAP(pv);
PMAP_LOCK(pmap);
pde = pmap_pde(pmap, pv->pv_va);
if ((*pde & (PG_M | PG_RW)) == (PG_M | PG_RW)) {
/*
* Although "*pde" is mapping a 2/4MB 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 either 1024
@ -4872,6 +4888,8 @@ pmap_ts_referenced(vm_page_t m)
("pmap_ts_referenced: found a 4mpage in page %p's pv list",
m));
pte = pmap_pte_quick(pmap, pv->pv_va);
if ((*pte & (PG_M | PG_RW)) == (PG_M | PG_RW))
vm_page_dirty(m);
if ((*pte & PG_A) != 0) {
atomic_clear_int((u_int *)pte, PG_A);
pmap_invalidate_page(pmap, pv->pv_va);