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);
}
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