svn commit: r300826 - head/sys/vm
Alan Cox
alc at FreeBSD.org
Fri May 27 06:05:14 UTC 2016
Author: alc
Date: Fri May 27 06:05:12 2016
New Revision: 300826
URL: https://svnweb.freebsd.org/changeset/base/300826
Log:
Use vm_page_replace_checked() instead of vm_page_rename() for implementing
optimized copy-on-write faults. This has two advantages: (1) one less radix
tree operation is performed and (2) vm_page_replace_checked() cannot fail,
making the code simpler.
Submitted by: Ryan Libby
Reviewed by: kib
Sponsored by: EMC / Isilon Storage Division
Differential Revision: https://reviews.freebsd.org/D4478
Modified:
head/sys/vm/vm_fault.c
Modified: head/sys/vm/vm_fault.c
==============================================================================
--- head/sys/vm/vm_fault.c Fri May 27 05:58:53 2016 (r300825)
+++ head/sys/vm/vm_fault.c Fri May 27 06:05:12 2016 (r300826)
@@ -799,26 +799,15 @@ vnode_locked:
* We don't chase down the shadow chain
*/
fs.object == fs.first_object->backing_object) {
- /*
- * get rid of the unnecessary page
- */
- vm_page_lock(fs.first_m);
- vm_page_remove(fs.first_m);
- vm_page_unlock(fs.first_m);
- /*
- * grab the page and put it into the
- * process'es object. The page is
- * automatically made dirty.
- */
- if (vm_page_rename(fs.m, fs.first_object,
- fs.first_pindex)) {
- VM_OBJECT_WUNLOCK(fs.first_object);
- unlock_and_deallocate(&fs);
- goto RetryFault;
- }
+ vm_page_lock(fs.m);
+ vm_page_remove(fs.m);
+ vm_page_unlock(fs.m);
vm_page_lock(fs.first_m);
+ vm_page_replace_checked(fs.m, fs.first_object,
+ fs.first_pindex, fs.first_m);
vm_page_free(fs.first_m);
vm_page_unlock(fs.first_m);
+ vm_page_dirty(fs.m);
#if VM_NRESERVLEVEL > 0
/*
* Rename the reservation.
@@ -827,6 +816,10 @@ vnode_locked:
fs.object, OFF_TO_IDX(
fs.first_object->backing_object_offset));
#endif
+ /*
+ * Removing the page from the backing object
+ * unbusied it.
+ */
vm_page_xbusy(fs.m);
fs.first_m = fs.m;
fs.m = NULL;
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