Author: kib
Date: Thu Jun 23 08:28:13 2016
New Revision: 302131
URL: https://svnweb.freebsd.org/changeset/base/302131

Log:
  In vm_page_xunbusy_maybelocked(), add fast path for unbusy when no
  waiters exist, same as for vm_page_xunbusy().  If previous value of
  busy_lock was VPB_SINGLE_EXCLUSIVER, no waiters existed and wakeup is
  not needed.
  
  Move common code from vm_page_xunbusy_maybelocked() and
  vm_page_xunbusy_hard() to vm_page_xunbusy_locked().
  
  Reviewed by:  alc
  Sponsored by: The FreeBSD Foundation
  MFC after:    2 weeks
  Approved by:  re (gjb)

Modified:
  head/sys/vm/vm_page.c

Modified: head/sys/vm/vm_page.c
==============================================================================
--- head/sys/vm/vm_page.c       Thu Jun 23 08:27:38 2016        (r302130)
+++ head/sys/vm/vm_page.c       Thu Jun 23 08:28:13 2016        (r302131)
@@ -760,17 +760,36 @@ vm_page_trysbusy(vm_page_t m)
 }
 
 static void
+vm_page_xunbusy_locked(vm_page_t m)
+{
+
+       vm_page_assert_xbusied(m);
+       vm_page_assert_locked(m);
+
+       atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
+       /* There is a waiter, do wakeup() instead of vm_page_flash(). */
+       wakeup(m);
+}
+
+static void
 vm_page_xunbusy_maybelocked(vm_page_t m)
 {
        bool lockacq;
 
        vm_page_assert_xbusied(m);
 
+       /*
+        * Fast path for unbusy.  If it succeeds, we know that there
+        * are no waiters, so we do not need a wakeup.
+        */
+       if (atomic_cmpset_rel_int(&m->busy_lock, VPB_SINGLE_EXCLUSIVER,
+           VPB_UNBUSIED))
+               return;
+
        lockacq = !mtx_owned(vm_page_lockptr(m));
        if (lockacq)
                vm_page_lock(m);
-       vm_page_flash(m);
-       atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
+       vm_page_xunbusy_locked(m);
        if (lockacq)
                vm_page_unlock(m);
 }
@@ -788,8 +807,7 @@ vm_page_xunbusy_hard(vm_page_t m)
        vm_page_assert_xbusied(m);
 
        vm_page_lock(m);
-       atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
-       wakeup(m);
+       vm_page_xunbusy_locked(m);
        vm_page_unlock(m);
 }
 
_______________________________________________
svn-src-all@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/svn-src-all
To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"

Reply via email to