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Date:      Wed, 1 Jun 2016 20:39:00 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r301165 - head/sys/vm
Message-ID:  <201606012039.u51Kd0Zs023339@repo.freebsd.org>
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Author: kib
Date: Wed Jun  1 20:39:00 2016
New Revision: 301165
URL: https://svnweb.freebsd.org/changeset/base/301165

Log:
  If the fast path unbusy in vm_page_replace() fails, slow path needs to
  acquire the page lock, which recurses.  Avoid the recursion by reusing
  the code from vm_page_remove() in a new helper
  vm_page_xunbusy_maybelocked().
  
  Reviewed by:	alc
  Sponsored by:	The FreeBSD Foundation

Modified:
  head/sys/vm/vm_page.c

Modified: head/sys/vm/vm_page.c
==============================================================================
--- head/sys/vm/vm_page.c	Wed Jun  1 20:30:31 2016	(r301164)
+++ head/sys/vm/vm_page.c	Wed Jun  1 20:39:00 2016	(r301165)
@@ -759,6 +759,22 @@ vm_page_trysbusy(vm_page_t m)
 	}
 }
 
+static void
+vm_page_xunbusy_maybelocked(vm_page_t m)
+{
+	bool lockacq;
+
+	vm_page_assert_xbusied(m);
+
+	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);
+	if (lockacq)
+		vm_page_unlock(m);
+}
+
 /*
  *	vm_page_xunbusy_hard:
  *
@@ -1197,25 +1213,14 @@ void
 vm_page_remove(vm_page_t m)
 {
 	vm_object_t object;
-	boolean_t lockacq;
 
 	if ((m->oflags & VPO_UNMANAGED) == 0)
-		vm_page_lock_assert(m, MA_OWNED);
+		vm_page_assert_locked(m);
 	if ((object = m->object) == NULL)
 		return;
 	VM_OBJECT_ASSERT_WLOCKED(object);
-	if (vm_page_xbusied(m)) {
-		lockacq = FALSE;
-		if ((m->oflags & VPO_UNMANAGED) != 0 &&
-		    !mtx_owned(vm_page_lockptr(m))) {
-			lockacq = TRUE;
-			vm_page_lock(m);
-		}
-		vm_page_flash(m);
-		atomic_store_rel_int(&m->busy_lock, VPB_UNBUSIED);
-		if (lockacq)
-			vm_page_unlock(m);
-	}
+	if (vm_page_xbusied(m))
+		vm_page_xunbusy_maybelocked(m);
 
 	/*
 	 * Now remove from the object's list of backed pages.
@@ -1340,7 +1345,7 @@ vm_page_replace(vm_page_t mnew, vm_objec
 	TAILQ_REMOVE(&object->memq, mold, listq);
 
 	mold->object = NULL;
-	vm_page_xunbusy(mold);
+	vm_page_xunbusy_maybelocked(mold);
 
 	/*
 	 * The object's resident_page_count does not change because we have

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