[src/sommerfeld_i386mp_1]: src/sys/arch/i386/i386 Use optimisitc locking in p...

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/089ba692518b
branches:  sommerfeld_i386mp_1
changeset: 482389:089ba692518b
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Fri May 04 20:19:57 2001 +0000

description:
Use optimisitc locking in pmap_create() so that we don't lock against
ourself if allocating the page directory causes pmap_growkernel() to
be called.

diffstat:

 sys/arch/i386/i386/pmap.c |  21 +++++++++++++++------
 1 files changed, 15 insertions(+), 6 deletions(-)

diffs (60 lines):

diff -r 81fb68ab04c5 -r 089ba692518b sys/arch/i386/i386/pmap.c
--- a/sys/arch/i386/i386/pmap.c Fri May 04 01:32:58 2001 +0000
+++ b/sys/arch/i386/i386/pmap.c Fri May 04 20:19:57 2001 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pmap.c,v 1.83.2.34 2001/05/04 01:32:58 thorpej Exp $   */
+/*     $NetBSD: pmap.c,v 1.83.2.35 2001/05/04 20:19:57 thorpej Exp $   */
 
 /*
  *
@@ -414,6 +414,7 @@
 
 struct pool pmap_pdp_pool;
 struct pool_cache pmap_pdp_cache;
+u_int pmap_pdp_cache_generation;
 
 int    pmap_pdp_ctor(void *, void *, int);
 
@@ -1677,6 +1678,7 @@
 pmap_create()
 {
        struct pmap *pmap;
+       u_int gen;
 
        pmap = pool_get(&pmap_pmap_pool, PR_WAITOK);
 
@@ -1704,15 +1706,21 @@
         * malloc since malloc allocates out of a submap and we should
         * have already allocated kernel PTPs to cover the range...
         *
-        * NOTE: WE MUST NOT BLOCK WHILE HOLDING THE `pmap_lock'!
+        * NOTE: WE MUST NOT BLOCK WHILE HOLDING THE `pmap_lock', nor
+        * must we call pmap_growkernel() while holding it!
         */
 
+ try_again:
+       gen = pmap_pdp_cache_generation;
+       pmap->pm_pdir = pool_cache_get(&pmap_pdp_cache, PR_WAITOK);
+
        simple_lock(&pmaps_lock);
 
-       /* XXX Need a generic "I want memory" wchan */
-       while ((pmap->pm_pdir =
-           pool_cache_get(&pmap_pdp_cache, PR_NOWAIT)) == NULL)
-               (void) ltsleep(&lbolt, PVM, "pmapcr", hz >> 3, &pmaps_lock);
+       if (gen != pmap_pdp_cache_generation) {
+               simple_unlock(&pmaps_lock);
+               pool_cache_destruct_object(&pmap_pdp_cache, pmap->pm_pdir);
+               goto try_again;
+       }
 
        pmap->pm_pdirpa = pmap->pm_pdir[PDSLOT_PTE] & PG_FRAME;
 
@@ -3215,6 +3223,7 @@
 
                /* Invalidate the PDP cache. */
                pool_cache_invalidate(&pmap_pdp_cache);
+               pmap_pdp_cache_generation++;
 
                simple_unlock(&pmaps_lock);
        }