[src/uebayasi-xip]: src/sys/uvm Put comments why device pages skip some code ...

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

details:   https://anonhg.NetBSD.org/src/rev/6335a703fc59
branches:  uebayasi-xip
changeset: 751617:6335a703fc59
user:      uebayasi <uebayasi%NetBSD.org@localhost>
date:      Sun Feb 28 06:52:12 2010 +0000

description:
Put comments why device pages skip some code paths.  Don't skip accounting
for "neighbor" device pages.

diffstat:

 sys/uvm/uvm_fault.c |  28 +++++++++++++++++++---------
 1 files changed, 19 insertions(+), 9 deletions(-)

diffs (80 lines):

diff -r 84dd35ccd726 -r 6335a703fc59 sys/uvm/uvm_fault.c
--- a/sys/uvm/uvm_fault.c       Sun Feb 28 06:29:19 2010 +0000
+++ b/sys/uvm/uvm_fault.c       Sun Feb 28 06:52:12 2010 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_fault.c,v 1.166.2.5 2010/02/24 16:22:58 uebayasi Exp $     */
+/*     $NetBSD: uvm_fault.c,v 1.166.2.6 2010/02/28 06:52:12 uebayasi Exp $     */
 
 /*
  *
@@ -39,7 +39,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_fault.c,v 1.166.2.5 2010/02/24 16:22:58 uebayasi Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_fault.c,v 1.166.2.6 2010/02/28 06:52:12 uebayasi Exp $");
 
 #include "opt_uvmhist.h"
 #include "opt_device_page.h"
@@ -1769,10 +1769,6 @@
        mutex_enter(&uvm_pageqlock);
        uvm_pageenqueue(pg);
        mutex_exit(&uvm_pageqlock);
-       UVMHIST_LOG(maphist,
-           "  MAPPING: n obj: pm=0x%x, va=0x%x, pg=0x%x",
-           ufi->orig_map->pmap, currva, pg, 0);
-       uvmexp.fltnomap++;
 
        /*
         * Since this page isn't the page that's actually faulting,
@@ -1790,6 +1786,11 @@
        UVM_PAGE_OWN(pg, NULL);
 
 uvm_fault_lower_neighbor_enter:
+       UVMHIST_LOG(maphist,
+           "  MAPPING: n obj: pm=0x%x, va=0x%x, pg=0x%x",
+           ufi->orig_map->pmap, currva, pg, 0);
+       uvmexp.fltnomap++;
+
        (void) pmap_enter(ufi->orig_map->pmap, currva,
            VM_PAGE_TO_PHYS(pg),
            readonly ? (flt->enter_prot & ~VM_PROT_WRITE) :
@@ -1962,8 +1963,10 @@
        pg = uobjpage;          /* map in the actual object */
        uvmexp.flt_obj++;
 
-       if (uvm_pageisdevice_p(uobjpage))
+       if (uvm_pageisdevice_p(uobjpage)) {
+               /* XIP'ed device pages are always read-only */
                goto uvm_fault_lower_direct_done;
+       }
 
        if (UVM_ET_ISCOPYONWRITE(ufi->entry) ||
            UVM_OBJ_NEEDS_WRITEFAULT(uobjpage->uobject))
@@ -2094,8 +2097,13 @@
                         */
                }
 
-               if (uvm_pageisdevice_p(uobjpage))
+               if (uvm_pageisdevice_p(uobjpage)) {
+                       /*
+                        * XIP devices pages are never paged out, no need to
+                        * dispose.
+                        */
                        goto uvm_fault_lower_promote_done;
+               }
 
                /*
                 * dispose of uobjpage.  it can't be PG_RELEASED
@@ -2176,8 +2184,10 @@
            (flt->enter_prot & ~VM_PROT_WRITE) : flt->enter_prot,
            flt->access_type | PMAP_CANFAIL | (flt->wire_mapping ? PMAP_WIRED : 0)) != 0) {
 
-               if (uvm_pageisdevice_p(pg))
+               if (uvm_pageisdevice_p(pg)) {
+                       /* Device pages never involve paging activity. */
                        goto uvm_fault_lower_enter_error_done;
+               }
 
                /*
                 * No need to undo what we did; we can simply think of