[src/trunk]: src/sys/arch/i386/i386 merge in a bit from the MP branch to cut ...

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

details:   https://anonhg.NetBSD.org/src/rev/ada89b0a24d5
branches:  trunk
changeset: 520043:ada89b0a24d5
user:      chs <chs%NetBSD.org@localhost>
date:      Tue Jan 01 22:52:11 2002 +0000

description:
merge in a bit from the MP branch to cut down on LOCKDEBUG spew:
Use optimistic 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 |  24 +++++++++++++++++-------
 1 files changed, 17 insertions(+), 7 deletions(-)

diffs (70 lines):

diff -r 097723bd34b1 -r ada89b0a24d5 sys/arch/i386/i386/pmap.c
--- a/sys/arch/i386/i386/pmap.c Tue Jan 01 22:51:10 2002 +0000
+++ b/sys/arch/i386/i386/pmap.c Tue Jan 01 22:52:11 2002 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pmap.c,v 1.131 2001/11/15 07:03:30 lukem Exp $ */
+/*     $NetBSD: pmap.c,v 1.132 2002/01/01 22:52:11 chs Exp $   */
 
 /*
  *
@@ -60,7 +60,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.131 2001/11/15 07:03:30 lukem Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.132 2002/01/01 22:52:11 chs Exp $");
 
 #include "opt_cputype.h"
 #include "opt_user_ldt.h"
@@ -353,6 +353,7 @@
 
 struct pool pmap_pdp_pool;
 struct pool_cache pmap_pdp_cache;
+u_int pmap_pdp_cache_generation;
 
 int    pmap_pdp_ctor(void *, void *, int);
 
@@ -1452,6 +1453,7 @@
 pmap_create()
 {
        struct pmap *pmap;
+       u_int gen;
 
        pmap = pool_get(&pmap_pmap_pool, PR_WAITOK);
 
@@ -1479,15 +1481,21 @@
         * 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;
 
@@ -2993,6 +3001,8 @@
 
                /* Invalidate the PDP cache. */
                pool_cache_invalidate(&pmap_pdp_cache);
+               pmap_pdp_cache_generation++;
+
                simple_unlock(&pmaps_lock);
        }