[src/yamt-pagecache]: src/sys/uvm uvn_findpage: fix dense case. add comments.

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

details:   https://anonhg.NetBSD.org/src/rev/a3ffe1b422c3
branches:  yamt-pagecache
changeset: 770892:a3ffe1b422c3
user:      yamt <yamt%NetBSD.org@localhost>
date:      Fri Nov 02 08:26:33 2012 +0000

description:
uvn_findpage: fix dense case.  add comments.

diffstat:

 sys/uvm/uvm_vnode.c |  21 ++++++++++++++++++---
 1 files changed, 18 insertions(+), 3 deletions(-)

diffs (57 lines):

diff -r e4189f682617 -r a3ffe1b422c3 sys/uvm/uvm_vnode.c
--- a/sys/uvm/uvm_vnode.c       Fri Nov 02 08:22:33 2012 +0000
+++ b/sys/uvm/uvm_vnode.c       Fri Nov 02 08:26:33 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_vnode.c,v 1.97.2.8 2012/10/30 17:23:03 yamt Exp $  */
+/*     $NetBSD: uvm_vnode.c,v 1.97.2.9 2012/11/02 08:26:33 yamt Exp $  */
 
 /*
  * Copyright (c) 1997 Charles D. Cranor and Washington University.
@@ -45,7 +45,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_vnode.c,v 1.97.2.8 2012/10/30 17:23:03 yamt Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_vnode.c,v 1.97.2.9 2012/11/02 08:26:33 yamt Exp $");
 
 #include "opt_uvmhist.h"
 
@@ -242,6 +242,13 @@
        return (found);
 }
 
+/*
+ * uvn_findpage: find a single page
+ *
+ * if a suitable page was found, put it in *pgp and return 1.
+ * otherwise return 0.
+ */
+
 static int
 uvn_findpage(struct uvm_object *uobj, voff_t offset, struct vm_page **pgp,
     unsigned int flags, struct uvm_page_array *a, unsigned int nleft)
@@ -269,7 +276,7 @@
                 * uvn_findpages.  in that case, fillflags used by the caller
                 * might not match strictly with ours.
                 * in particular, the caller might have filled the array
-                * without DIRTYONLY or DENSE but passed us UFP_DIRTYONLY.
+                * without DENSE but passed us UFP_DIRTYONLY (thus DENSE).
                 */
                pg = uvm_page_array_fill_and_peek(a, uobj, offset, nleft,
                    fillflags);
@@ -277,7 +284,15 @@
                        KASSERT(
                            ((fillflags & UVM_PAGE_ARRAY_FILL_BACKWARD) != 0)
                            == (pg->offset < offset));
+                       KASSERT(uvm_pagelookup(uobj, offset) == NULL
+                           || ((fillflags & UVM_PAGE_ARRAY_FILL_DIRTY) != 0 &&
+                           radix_tree_get_tag(&uobj->uo_pages,
+                           offset >> PAGE_SHIFT, UVM_PAGE_DIRTY_TAG) == 0));
                        pg = NULL;
+                       if ((fillflags & UVM_PAGE_ARRAY_FILL_DENSE) != 0) {
+                               UVMHIST_LOG(ubchist, "dense", 0,0,0,0);
+                               return 0;
+                       }
                }
 
                /* nope?  allocate one now */