Date: Sat, 06 Aug 2005 20:12:55 -0700 From: Julian Elischer <julian@elischer.org> To: Martin Nilsson <martin@gneto.com> Cc: freebsd-current@freebsd.org Subject: Re: Something is very wrong with disk caching in 7.0 Message-ID: <42F57C37.3080900@elischer.org> In-Reply-To: <42F4730C.6040204@gneto.com> References: <42F45923.2080401@gneto.com> <42F4659F.5030407@gneto.com> <42F46942.7030005@elischer.org> <42F4730C.6040204@gneto.com>
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Martin Nilsson wrote:
> Julian Elischer wrote:
>
try this patch
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Index: sys/vm/vm_pageout.c
===================================================================
RCS file: /home/ncvs/src/sys/vm/vm_pageout.c,v
retrieving revision 1.268
diff -u -r1.268 vm_pageout.c
--- sys/vm/vm_pageout.c 7 Jan 2005 02:29:27 -0000 1.268
+++ sys/vm/vm_pageout.c 30 Jul 2005 03:12:37 -0000
@@ -5,6 +5,8 @@
* All rights reserved.
* Copyright (c) 1994 David Greenman
* All rights reserved.
+ * Copyright (c) 2005 Yahoo! Technologies Norway AS
+ * All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* The Mach Operating System project at Carnegie-Mellon University.
@@ -210,6 +212,16 @@
static void vm_pageout_page_stats(void);
/*
+ * Experimental VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK option, which will cause
+ * pagedaemon to fall back to blocking locking of vm objects if nonblocking
+ * lock attempt failed. Lock order violation is avoided by unlocking
+ * the page queues before locking the object. marker pages are used
+ * to detect changes and allow for continued page queue traversal even
+ * when changes had occurred.
+ */
+#define VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+
+/*
* vm_pageout_clean:
*
* Clean the page and remove it from the laundry.
@@ -750,8 +762,37 @@
* queue, most likely are being paged out.
*/
if (!VM_OBJECT_TRYLOCK(object)) {
+#ifdef VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+ /*
+ * Cannot lock object while holding page queue lock.
+ * Depend on both struct vm_object and normal
+ * struct vm_page being type stable and sanity
+ * check after reobtaining page queue lock.
+ */
+ TAILQ_INSERT_AFTER(&vm_page_queues[PQ_INACTIVE].pl,
+ m, &marker, pageq);
+ vm_page_unlock_queues();
+ VM_OBJECT_LOCK(object);
+ vm_page_lock_queues();
+ /* Page queue might have changed. */
+ next = TAILQ_NEXT(&marker, pageq);
+ if (m->queue != PQ_INACTIVE ||
+ m->object != object ||
+ m->hold_count != 0 ||
+ &marker != TAILQ_NEXT(m, pageq)) {
+ /* Page changed. */
+ VM_OBJECT_UNLOCK(object);
+ TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE].pl,
+ &marker, pageq);
+ addl_page_shortage++;
+ continue;
+ }
+ TAILQ_REMOVE(&vm_page_queues[PQ_INACTIVE].pl,
+ &marker, pageq);
+#else
addl_page_shortage++;
continue;
+#endif
}
if (m->busy || (m->flags & PG_BUSY)) {
VM_OBJECT_UNLOCK(object);
@@ -1024,10 +1065,44 @@
next = TAILQ_NEXT(m, pageq);
object = m->object;
+#ifdef VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+ if ((m->flags & PG_MARKER) != 0) {
+ m = next;
+ continue;
+ }
+#endif
if (!VM_OBJECT_TRYLOCK(object)) {
+#ifdef VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+ /*
+ * Cannot lock object while holding page queue lock.
+ * Depend on both struct vm_object and normal
+ * struct vm_page being type stable and sanity
+ * check after reobtaining page queue lock.
+ */
+ TAILQ_INSERT_AFTER(&vm_page_queues[PQ_ACTIVE].pl,
+ m, &marker, pageq);
+ vm_page_unlock_queues();
+ VM_OBJECT_LOCK(object);
+ vm_page_lock_queues();
+ /* Page queue might have changed. */
+ next = TAILQ_NEXT(&marker, pageq);
+ if (m->queue != PQ_ACTIVE ||
+ m->object != object ||
+ &marker != TAILQ_NEXT(m, pageq)) {
+ /* Page changed. */
+ VM_OBJECT_UNLOCK(object);
+ TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE].pl,
+ &marker, pageq);
+ m = next;
+ continue;
+ }
+ TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE].pl,
+ &marker, pageq);
+#else
vm_pageq_requeue(m);
m = next;
continue;
+#endif
}
/*
@@ -1264,6 +1339,9 @@
vm_pageout_page_stats()
{
vm_object_t object;
+#ifdef VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+ struct vm_page marker;
+#endif
vm_page_t m,next;
int pcount,tpcount; /* Number of pages to check */
static int fullintervalcount = 0;
@@ -1287,6 +1365,16 @@
fullintervalcount = 0;
}
+#ifdef VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+ /*
+ * Initialize our marker
+ */
+ bzero(&marker, sizeof(marker));
+ marker.flags = PG_BUSY | PG_FICTITIOUS | PG_MARKER;
+ marker.queue = PQ_INACTIVE;
+ marker.wire_count = 1;
+#endif
+
m = TAILQ_FIRST(&vm_page_queues[PQ_ACTIVE].pl);
while ((m != NULL) && (pcount-- > 0)) {
int actcount;
@@ -1296,10 +1384,45 @@
next = TAILQ_NEXT(m, pageq);
object = m->object;
+
+#ifdef VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+ if ((m->flags & PG_MARKER) != 0) {
+ m = next;
+ continue;
+ }
+#endif
if (!VM_OBJECT_TRYLOCK(object)) {
+#ifdef VM_PAGEOUT_FORCE_BLOCKING_OBJLOCK
+ /*
+ * Cannot lock object while holding page queue lock.
+ * Depend on both struct vm_object and normal
+ * struct vm_page being type stable and sanity
+ * check after reobtaining page queue lock.
+ */
+ TAILQ_INSERT_AFTER(&vm_page_queues[PQ_ACTIVE].pl,
+ m, &marker, pageq);
+ vm_page_unlock_queues();
+ VM_OBJECT_LOCK(object);
+ vm_page_lock_queues();
+ /* Page queue might have changed. */
+ next = TAILQ_NEXT(&marker, pageq);
+ if (m->queue != PQ_ACTIVE ||
+ m->object != object ||
+ &marker != TAILQ_NEXT(m, pageq)) {
+ /* Page changed. */
+ VM_OBJECT_UNLOCK(object);
+ TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE].pl,
+ &marker, pageq);
+ m = next;
+ continue;
+ }
+ TAILQ_REMOVE(&vm_page_queues[PQ_ACTIVE].pl,
+ &marker, pageq);
+#else
vm_pageq_requeue(m);
m = next;
continue;
+#endif
}
/*
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