[src/trunk]: src/sys/uvm - ubc_uiomove(): Always use direct access in the UB...

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

details:   https://anonhg.NetBSD.org/src/rev/df989d866a81
branches:  trunk
changeset: 933333:df989d866a81
user:      ad <ad%NetBSD.org@localhost>
date:      Sun May 24 20:05:53 2020 +0000

description:
- ubc_uiomove():  Always use direct access in the UBC_FAULTBUSY case, since
  it works basically the same way as !direct minus temporary mappings, and
  there are no concurrency issues.

- ubc_alloc_direct(): In the PGO_OVERWRITE case blocks are allocated
  beforehand.  Avoid waking or activating pages unless needed.

diffstat:

 sys/uvm/uvm_bio.c |  30 ++++++++++++++++++++----------
 1 files changed, 20 insertions(+), 10 deletions(-)

diffs (73 lines):

diff -r d1ae61c7aedc -r df989d866a81 sys/uvm/uvm_bio.c
--- a/sys/uvm/uvm_bio.c Sun May 24 19:58:02 2020 +0000
+++ b/sys/uvm/uvm_bio.c Sun May 24 20:05:53 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: uvm_bio.c,v 1.115 2020/05/23 11:59:03 ad Exp $ */
+/*     $NetBSD: uvm_bio.c,v 1.116 2020/05/24 20:05:53 ad Exp $ */
 
 /*
  * Copyright (c) 1998 Chuck Silvers.
@@ -34,7 +34,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_bio.c,v 1.115 2020/05/23 11:59:03 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_bio.c,v 1.116 2020/05/24 20:05:53 ad Exp $");
 
 #include "opt_uvmhist.h"
 #include "opt_ubc.h"
@@ -748,9 +748,13 @@
         *
         * avoid the problem by disallowing direct access if the object
         * might be visible somewhere via mmap().
+        *
+        * XXX concurrent reads cause thundering herd issues with PG_BUSY. 
+        * In the future enable by default for writes or if ncpu<=2, and
+        * make the toggle override that.
         */
-
-       if (ubc_direct && (flags & UBC_ISMAPPED) == 0) {
+       if ((ubc_direct && (flags & UBC_ISMAPPED) == 0) ||
+           (flags & UBC_FAULTBUSY) != 0) {
                return ubc_uiomove_direct(uobj, uio, todo, advice, flags);
        }
 #endif
@@ -841,7 +845,7 @@
 
        if (flags & UBC_WRITE) {
                if (flags & UBC_FAULTBUSY)
-                       gpflags |= PGO_OVERWRITE;
+                       gpflags |= PGO_OVERWRITE | PGO_NOBLOCKALLOC;
 #if 0
                KASSERT(!UVM_OBJ_NEEDS_WRITEFAULT(uobj));
 #endif
@@ -902,7 +906,10 @@
                /* Page must be writable by now */
                KASSERT((pg->flags & PG_RDONLY) == 0 || (flags & UBC_WRITE) == 0);
 
-               /* No managed mapping - mark the page dirty. */
+               /*
+                * XXX For aobj pages.  No managed mapping - mark the page
+                * dirty.
+                */
                if ((flags & UBC_WRITE) != 0) {
                        uvm_pagemarkdirty(pg, UVM_PAGE_STATUS_DIRTY);   
                }
@@ -927,10 +934,13 @@
                        uvm_pagefree(pg);
                        continue;
                }
-               uvm_pagelock(pg);
-               uvm_pageactivate(pg);
-               uvm_pagewakeup(pg);
-               uvm_pageunlock(pg);
+
+               if (uvm_pagewanted_p(pg) || uvmpdpol_pageactivate_p(pg)) {
+                       uvm_pagelock(pg);
+                       uvm_pageactivate(pg);
+                       uvm_pagewakeup(pg);
+                       uvm_pageunlock(pg);
+               }
 
                /* Page was changed, no longer fake and neither clean. */
                if (flags & UBC_WRITE) {