svn commit: r207205 - in head/sys: amd64/amd64 i386/i386
Alan Cox
alc at FreeBSD.org
Sun Apr 25 20:40:46 UTC 2010
Author: alc
Date: Sun Apr 25 20:40:45 2010
New Revision: 207205
URL: http://svn.freebsd.org/changeset/base/207205
Log:
Clearing a page table entry's accessed bit (PG_A) and setting the
page's PG_REFERENCED flag in pmap_protect() can't really be justified.
In contrast to pmap_remove() or pmap_remove_all(), the mapping is not
being destroyed, so the notion that the page was accessed is not lost.
Moreover, clearing the page table entry's accessed bit and setting the
page's PG_REFERENCED flag can throw off the page daemon's activity
count calculation. Finally, in my tests, I found that 15% of the
atomic memory operations being performed by pmap_protect() were only
to clear PG_A, and not change protection. This could, by itself, be
fixed, but I don't see the point given the above argument.
Remove a comment from pmap_protect_pde() that is no longer meaningful
after the above change.
Modified:
head/sys/amd64/amd64/pmap.c
head/sys/i386/i386/pmap.c
Modified: head/sys/amd64/amd64/pmap.c
==============================================================================
--- head/sys/amd64/amd64/pmap.c Sun Apr 25 20:01:13 2010 (r207204)
+++ head/sys/amd64/amd64/pmap.c Sun Apr 25 20:40:45 2010 (r207205)
@@ -2833,18 +2833,9 @@ retry:
if (oldpde & PG_MANAGED) {
eva = sva + NBPDR;
for (va = sva, m = PHYS_TO_VM_PAGE(oldpde & PG_PS_FRAME);
- va < eva; va += PAGE_SIZE, m++) {
- /*
- * In contrast to the analogous operation on a 4KB page
- * mapping, the mapping's PG_A flag is not cleared and
- * the page's PG_REFERENCED flag is not set. The
- * reason is that pmap_demote_pde() expects that a 2MB
- * page mapping with a stored page table page has PG_A
- * set.
- */
+ va < eva; va += PAGE_SIZE, m++)
if ((oldpde & (PG_M | PG_RW)) == (PG_M | PG_RW))
vm_page_dirty(m);
- }
}
if ((prot & VM_PROT_WRITE) == 0)
newpde &= ~(PG_RW | PG_M);
@@ -2953,23 +2944,15 @@ retry:
obits = pbits = *pte;
if ((pbits & PG_V) == 0)
continue;
- if (pbits & PG_MANAGED) {
- m = NULL;
- if (pbits & PG_A) {
+
+ if ((prot & VM_PROT_WRITE) == 0) {
+ if ((pbits & (PG_MANAGED | PG_M | PG_RW)) ==
+ (PG_MANAGED | PG_M | PG_RW)) {
m = PHYS_TO_VM_PAGE(pbits & PG_FRAME);
- vm_page_flag_set(m, PG_REFERENCED);
- pbits &= ~PG_A;
- }
- if ((pbits & (PG_M | PG_RW)) == (PG_M | PG_RW)) {
- if (m == NULL)
- m = PHYS_TO_VM_PAGE(pbits &
- PG_FRAME);
vm_page_dirty(m);
}
- }
-
- if ((prot & VM_PROT_WRITE) == 0)
pbits &= ~(PG_RW | PG_M);
+ }
if ((prot & VM_PROT_EXECUTE) == 0)
pbits |= pg_nx;
Modified: head/sys/i386/i386/pmap.c
==============================================================================
--- head/sys/i386/i386/pmap.c Sun Apr 25 20:01:13 2010 (r207204)
+++ head/sys/i386/i386/pmap.c Sun Apr 25 20:40:45 2010 (r207205)
@@ -2955,18 +2955,9 @@ retry:
if (oldpde & PG_MANAGED) {
eva = sva + NBPDR;
for (va = sva, m = PHYS_TO_VM_PAGE(oldpde & PG_PS_FRAME);
- va < eva; va += PAGE_SIZE, m++) {
- /*
- * In contrast to the analogous operation on a 4KB page
- * mapping, the mapping's PG_A flag is not cleared and
- * the page's PG_REFERENCED flag is not set. The
- * reason is that pmap_demote_pde() expects that a 2/4MB
- * page mapping with a stored page table page has PG_A
- * set.
- */
+ va < eva; va += PAGE_SIZE, m++)
if ((oldpde & (PG_M | PG_RW)) == (PG_M | PG_RW))
vm_page_dirty(m);
- }
}
if ((prot & VM_PROT_WRITE) == 0)
newpde &= ~(PG_RW | PG_M);
@@ -3074,22 +3065,15 @@ retry:
obits = pbits = *pte;
if ((pbits & PG_V) == 0)
continue;
- if (pbits & PG_MANAGED) {
- m = NULL;
- if (pbits & PG_A) {
+
+ if ((prot & VM_PROT_WRITE) == 0) {
+ if ((pbits & (PG_MANAGED | PG_M | PG_RW)) ==
+ (PG_MANAGED | PG_M | PG_RW)) {
m = PHYS_TO_VM_PAGE(pbits & PG_FRAME);
- vm_page_flag_set(m, PG_REFERENCED);
- pbits &= ~PG_A;
- }
- if ((pbits & (PG_M | PG_RW)) == (PG_M | PG_RW)) {
- if (m == NULL)
- m = PHYS_TO_VM_PAGE(pbits & PG_FRAME);
vm_page_dirty(m);
}
- }
-
- if ((prot & VM_PROT_WRITE) == 0)
pbits &= ~(PG_RW | PG_M);
+ }
#ifdef PAE
if ((prot & VM_PROT_EXECUTE) == 0)
pbits |= pg_nx;
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