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With the new-and-improved vm_fault_copy_entry() (r265843), we can always

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avoid soft page faults when adding write access to user wired entries in
vm_map_protect().  Previously, we only avoided the soft page fault when
the underlying pages were copy-on-write.  In other words, we avoided the
pages faults that might sleep on page allocation, but not the trivial
page faults to update the physical map.

Reviewed by:	kib
MFC after:	1 week
Sponsored by:	EMC / Isilon Storage Division
This commit is contained in:
Alan Cox 2014-05-11 17:41:29 +00:00
parent 30238f4963
commit dd006a1b14
1 changed files with 9 additions and 2 deletions
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11
sys/vm/vm_map.c
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@ -1978,10 +1978,17 @@ vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
else
current->protection = new_prot;
if ((current->eflags & (MAP_ENTRY_COW | MAP_ENTRY_USER_WIRED))
== (MAP_ENTRY_COW | MAP_ENTRY_USER_WIRED) &&
/*
* For user wired map entries, the normal lazy evaluation of
* write access upgrades through soft page faults is
* undesirable. Instead, immediately copy any pages that are
* copy-on-write and enable write access in the physical map.
*/
if ((current->eflags & MAP_ENTRY_USER_WIRED) != 0 &&
(current->protection & VM_PROT_WRITE) != 0 &&
(old_prot & VM_PROT_WRITE) == 0) {
KASSERT(old_prot != VM_PROT_NONE,
("vm_map_protect: inaccessible wired map entry"));
vm_fault_copy_entry(map, map, current, current, NULL);
}