Page MenuHomeFreeBSD
Files F143959714

D19065.id53562.diff
No OneTemporary
Actions

D19065.id53562.diff
View Options

Index: sys/vm/vm_page.h
===================================================================
--- sys/vm/vm_page.h
+++ sys/vm/vm_page.h
@@ -351,8 +351,10 @@
* queue, and cleared when the dequeue request is processed. A page may
* have PGA_DEQUEUE set and PGA_ENQUEUED cleared, for instance if a dequeue
* is requested after the page is scheduled to be enqueued but before it is
- * actually inserted into the page queue. The page lock must be held to set
- * this flag, and the queue lock for the page must be held to clear it.
+ * actually inserted into the page queue. For allocated pages, the page lock
+ * must be held to set this flag, but it may be set by vm_page_free_prep()
+ * without the page lock held. The page queue lock must be held to clear the
+ * PGA_DEQUEUE flag.
*
* PGA_REQUEUE is set when the page is scheduled to be enqueued or requeued
* in its page queue. The page lock must be held to set this flag, and the
Index: sys/vm/vm_page.c
===================================================================
--- sys/vm/vm_page.c
+++ sys/vm/vm_page.c
@@ -3175,7 +3175,11 @@
struct vm_pagequeue *pq;
int domain;
- vm_page_assert_locked(m);
+ KASSERT((m->oflags & VPO_UNMANAGED) == 0,
+ ("page %p is unmanaged", m));
+ KASSERT(mtx_owned(vm_page_lockptr(m)) ||
+ (m->object == NULL && (m->aflags & PGA_DEQUEUE) != 0),
+ ("missing synchronization for page %p", m));
KASSERT(queue < PQ_COUNT, ("invalid queue %d", queue));
domain = vm_phys_domain(m);
@@ -3197,8 +3201,9 @@
/*
* The page may have been logically dequeued before we acquired the
- * page queue lock. In this case, the page lock prevents the page
- * from being logically enqueued elsewhere.
+ * page queue lock. In this case, since we either hold the page lock
+ * or the page is being freed, a different thread cannot be concurrently
+ * enqueuing the page.
*/
if (__predict_true(m->queue == queue))
vm_pqbatch_process_page(pq, m);
@@ -3289,6 +3294,30 @@
vm_pqbatch_submit_page(m, queue);
}
+/*
+ * A variant of vm_page_dequeue_deferred() that does not assert the page
+ * lock and is only to be called from vm_page_free_prep(). It is just an
+ * open-coded implementation of vm_page_dequeue_deferred(). Because the
+ * page is being freed, we can assume that nothing else is scheduling queue
+ * operations on this page, so we get for free the mutual exclusion that
+ * is otherwise provided by the page lock.
+ */
+static void
+vm_page_dequeue_deferred_free(vm_page_t m)
+{
+ uint8_t queue;
+
+ KASSERT(m->object == NULL, ("page %p has an object reference", m));
+
+ if ((m->aflags & PGA_DEQUEUE) != 0)
+ return;
+ atomic_thread_fence_acq();
+ if ((queue = m->queue) == PQ_NONE)
+ return;
+ vm_page_aflag_set(m, PGA_DEQUEUE);
+ vm_pqbatch_submit_page(m, queue);
+}
+
/*
* vm_page_dequeue:
*
@@ -3474,7 +3503,7 @@
* dequeue.
*/
if ((m->oflags & VPO_UNMANAGED) == 0)
- vm_page_dequeue_deferred(m);
+ vm_page_dequeue_deferred_free(m);
m->valid = 0;
vm_page_undirty(m);

File Metadata

Mime Type
text/plain
Expires
Tue, Feb 3, 2:34 PM (3 h, 34 m)
Storage Engine
blob
Storage Format
Raw Data
Storage Handle
28424752
Default Alt Text
D19065.id53562.diff (2 KB)

Event Timeline