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MFamd64 SVN rev 179749 CVS rev 1.620

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Reverse the direction of pmap_promote_pde()'s traversal over the specified
  page table page.  The direction of the traversal can matter if
  pmap_promote_pde() has to remove write access (PG_RW) from a PTE that
  hasn't been modified (PG_M).  In general, if there are two or more such
  PTEs to choose among, it is better to write protect the one nearer the
  high end of the page table page rather than the low end.  This is because
  most programs access memory in an ascending direction.  The net result of
  this change is a sometimes significant reduction in the number of failed
  promotion attempts and the number of pages that are write protected by
  pmap_promote_pde().

MFamd64 SVN rev 179777 CVS rev 1.621
  Tweak the promotion test in pmap_promote_pde().  Specifically, test PG_A
  before PG_M.  This sometimes prevents unnecessary removal of write access
  from a PTE.  Overall, the net result is fewer demotions and promotion
  failures.
This commit is contained in:
Alan Cox 2008-09-20 16:24:42 +00:00
parent b88a2fe170
commit 1628900be4
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=183207
1 changed files with 31 additions and 15 deletions
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46
sys/i386/i386/pmap.c
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@ -2861,10 +2861,10 @@ pmap_protect(pmap_t pmap, vm_offset_t sva, vm_offset_t eva, vm_prot_t prot)
/*
* Tries to promote the 512 or 1024, contiguous 4KB page mappings that are
* within a single page table page to a single 2- or 4MB page mapping. For
* promotion to occur, two conditions must be met: (1) the 4KB page mappings
* must map aligned, contiguous physical memory and (2) the 4KB page mappings
* must have identical characteristics.
* within a single page table page (PTP) to a single 2- or 4MB page mapping.
* For promotion to occur, two conditions must be met: (1) the 4KB page
* mappings must map aligned, contiguous physical memory and (2) the 4KB page
* mappings must have identical characteristics.
*
* Managed (PG_MANAGED) mappings within the kernel address space are not
* promoted. The reason is that kernel PDEs are replicated in each pmap but
@ -2876,15 +2876,21 @@ pmap_promote_pde(pmap_t pmap, pd_entry_t *pde, vm_offset_t va)
{
pd_entry_t newpde;
pmap_t allpmaps_entry;
pt_entry_t *firstpte, oldpte, *pte;
pt_entry_t *firstpte, oldpte, pa, *pte;
vm_offset_t oldpteva;
vm_paddr_t pa;
vm_page_t mpte;
PMAP_LOCK_ASSERT(pmap, MA_OWNED);
/*
* Examine the first PTE in the specified PTP. Abort if this PTE is
* either invalid, unused, or does not map the first 4KB physical page
* within a 2- or 4MB page.
*/
firstpte = vtopte(trunc_4mpage(va));
setpde:
newpde = *firstpte;
if ((newpde & (PG_A | PG_V)) != (PG_A | PG_V)) {
if ((newpde & ((PG_FRAME & PDRMASK) | PG_A | PG_V)) != (PG_A | PG_V)) {
pmap_pde_p_failures++;
CTR2(KTR_PMAP, "pmap_promote_pde: failure for va %#x"
" in pmap %p", va, pmap);
@ -2896,17 +2902,27 @@ pmap_promote_pde(pmap_t pmap, pd_entry_t *pde, vm_offset_t va)
" in pmap %p", va, pmap);
return;
}
if ((newpde & (PG_M | PG_RW)) == PG_RW)
if ((newpde & (PG_M | PG_RW)) == PG_RW) {
/*
* When PG_M is already clear, PG_RW can be cleared without
* a TLB invalidation.
*/
if (!atomic_cmpset_int((u_int *)firstpte, newpde, newpde &
~PG_RW))
goto setpde;
newpde &= ~PG_RW;
}
/*
* Check all the ptes before promotion
* Examine each of the other PTEs in the specified PTP. Abort if this
* PTE maps an unexpected 4KB physical page or does not have identical
* characteristics to the first PTE.
*/
pa = newpde & PG_PS_FRAME;
for (pte = firstpte; pte < firstpte + NPTEPG; pte++) {
retry:
pa = (newpde & (PG_PS_FRAME | PG_A | PG_V)) + NBPDR - PAGE_SIZE;
for (pte = firstpte + NPTEPG - 1; pte > firstpte; pte--) {
setpte:
oldpte = *pte;
if ((oldpte & PG_FRAME) != pa) {
if ((oldpte & (PG_FRAME | PG_A | PG_V)) != pa) {
pmap_pde_p_failures++;
CTR2(KTR_PMAP, "pmap_promote_pde: failure for va %#x"
" in pmap %p", va, pmap);
@ -2919,7 +2935,7 @@ pmap_promote_pde(pmap_t pmap, pd_entry_t *pde, vm_offset_t va)
*/
if (!atomic_cmpset_int((u_int *)pte, oldpte,
oldpte & ~PG_RW))
goto retry;
goto setpte;
oldpte &= ~PG_RW;
oldpteva = (oldpte & PG_FRAME & PDRMASK) |
(va & ~PDRMASK);
@ -2932,7 +2948,7 @@ pmap_promote_pde(pmap_t pmap, pd_entry_t *pde, vm_offset_t va)
" in pmap %p", va, pmap);
return;
}
pa += PAGE_SIZE;
pa -= PAGE_SIZE;
}
/*