[src/trunk]: src/sys/arch/x86/x86 PR kern/55268: tmpfs is slow

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details:   https://anonhg.NetBSD.org/src/rev/c0e8c2a0f367
branches:  trunk
changeset: 932782:c0e8c2a0f367
user:      ad <ad%NetBSD.org@localhost>
date:      Fri May 15 22:19:01 2020 +0000

description:
PR kern/55268: tmpfs is slow

pmap_clear_attrs(): if a brand new page with no mappings just zap pp_attrs.

diffstat:

 sys/arch/x86/x86/pmap.c |  18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diffs (39 lines):

diff -r 8b9054ff2901 -r c0e8c2a0f367 sys/arch/x86/x86/pmap.c
--- a/sys/arch/x86/x86/pmap.c   Fri May 15 22:17:45 2020 +0000
+++ b/sys/arch/x86/x86/pmap.c   Fri May 15 22:19:01 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pmap.c,v 1.389 2020/05/08 00:49:43 riastradh Exp $     */
+/*     $NetBSD: pmap.c,v 1.390 2020/05/15 22:19:01 ad Exp $    */
 
 /*
  * Copyright (c) 2008, 2010, 2016, 2017, 2019, 2020 The NetBSD Foundation, Inc.
@@ -130,7 +130,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.389 2020/05/08 00:49:43 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.390 2020/05/15 22:19:01 ad Exp $");
 
 #include "opt_user_ldt.h"
 #include "opt_lockdebug.h"
@@ -4567,7 +4567,19 @@
        pp = VM_PAGE_TO_PP(pg);
        pa = VM_PAGE_TO_PHYS(pg);
 
-       return pmap_pp_clear_attrs(pp, pa, clearbits);
+       /*
+        * If this is a new page, assert it has no mappings and simply zap
+        * the stored attributes without taking any locks.
+        */
+       if ((pg->flags & PG_FAKE) != 0) {
+               KASSERT(atomic_load_relaxed(&pp->pp_pte.pte_va) == 0);
+               KASSERT(atomic_load_relaxed(&pp->pp_pte.pte_ptp) == NULL);
+               KASSERT(atomic_load_relaxed(&pp->pp_pvlist.lh_first) == NULL);
+               atomic_store_relaxed(&pp->pp_attrs, 0);
+               return false;
+       } else {
+               return pmap_pp_clear_attrs(pp, pa, clearbits);
+       }
 }
 
 /*