uvm combine clearbits

[Ted Unangst]

uvm_pagefree calls atomic_clearbits_int too many times. Just
accumulate the flags we need to zap, then do it once.

Index: uvm_page.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_page.c,v
retrieving revision 1.122
diff -u -p -r1.122 uvm_page.c
--- uvm_page.c  12 Mar 2013 21:10:11 -0000      1.122
+++ uvm_page.c  26 Mar 2013 07:45:56 -0000
@@ -1053,6 +1053,7 @@ void
 uvm_pagefree(struct vm_page *pg)
 {
        int saved_loan_count = pg->loan_count;
+       u_int flags_to_clear = 0;
 
 #ifdef DEBUG
        if (pg->uobject == (void *)0xdeadbeef &&
@@ -1115,7 +1116,7 @@ uvm_pagefree(struct vm_page *pg)
 
        if (pg->pg_flags & PQ_ACTIVE) {
                TAILQ_REMOVE(&uvm.page_active, pg, pageq);
-               atomic_clearbits_int(&pg->pg_flags, PQ_ACTIVE);
+               flags_to_clear |= PQ_ACTIVE;
                uvmexp.active--;
        }
        if (pg->pg_flags & PQ_INACTIVE) {
@@ -1123,7 +1124,7 @@ uvm_pagefree(struct vm_page *pg)
                        TAILQ_REMOVE(&uvm.page_inactive_swp, pg, pageq);
                else
                        TAILQ_REMOVE(&uvm.page_inactive_obj, pg, pageq);
-               atomic_clearbits_int(&pg->pg_flags, PQ_INACTIVE);
+               flags_to_clear |= PQ_INACTIVE;
                uvmexp.inactive--;
        }
 
@@ -1138,15 +1139,16 @@ uvm_pagefree(struct vm_page *pg)
        if (pg->uanon) {
                pg->uanon->an_page = NULL;
                pg->uanon = NULL;
-               atomic_clearbits_int(&pg->pg_flags, PQ_ANON);
+               flags_to_clear |= PQ_ANON;
        }
 
        /*
         * Clean page state bits.
         */
-       atomic_clearbits_int(&pg->pg_flags, PQ_AOBJ); /* XXX: find culprit */
-       atomic_clearbits_int(&pg->pg_flags, PQ_ENCRYPT|
-           PG_ZERO|PG_FAKE|PG_BUSY|PG_RELEASED|PG_CLEAN|PG_CLEANCHK);
+       flags_to_clear |= PQ_AOBJ; /* XXX: find culprit */
+       flags_to_clear |= PQ_ENCRYPT|PG_ZERO|PG_FAKE|PG_BUSY|PG_RELEASED|
+           PG_CLEAN|PG_CLEANCHK;
+       atomic_clearbits_int(&pg->pg_flags, flags_to_clear);
 
        /*
         * and put on free queue