From 05e051bfe3217c74f0b53af172f01b0a6d902a04 Mon Sep 17 00:00:00 2001
From: markj <markj@FreeBSD.org>
Date: Fri, 13 Nov 2015 02:16:08 +0000
Subject: MFC r287235: Remove weighted page handling from vm_page_advise().

---
 sys/vm/vm_page.c | 79 ++++++++++++++++++--------------------------------------
 1 file changed, 25 insertions(+), 54 deletions(-)

(limited to 'sys/vm')

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 95bf6ca..243b11f 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -2430,19 +2430,26 @@ _vm_page_deactivate(vm_page_t m, int athead)
 	struct vm_pagequeue *pq;
 	int queue;
 
-	vm_page_lock_assert(m, MA_OWNED);
+	vm_page_assert_locked(m);
 
 	/*
-	 * Ignore if already inactive.
+	 * Ignore if the page is already inactive, unless it is unlikely to be
+	 * reactivated.
 	 */
-	if ((queue = m->queue) == PQ_INACTIVE)
+	if ((queue = m->queue) == PQ_INACTIVE && !athead)
 		return;
 	if (m->wire_count == 0 && (m->oflags & VPO_UNMANAGED) == 0) {
-		if (queue != PQ_NONE)
-			vm_page_dequeue(m);
-		m->flags &= ~PG_WINATCFLS;
 		pq = &vm_phys_domain(m)->vmd_pagequeues[PQ_INACTIVE];
-		vm_pagequeue_lock(pq);
+		/* Avoid multiple acquisitions of the inactive queue lock. */
+		if (queue == PQ_INACTIVE) {
+			vm_pagequeue_lock(pq);
+			vm_page_dequeue_locked(m);
+		} else {
+			if (queue != PQ_NONE)
+				vm_page_dequeue(m);
+			m->flags &= ~PG_WINATCFLS;
+			vm_pagequeue_lock(pq);
+		}
 		m->queue = PQ_INACTIVE;
 		if (athead)
 			TAILQ_INSERT_HEAD(&pq->pq_pl, m, plinks.q);
@@ -2618,34 +2625,18 @@ vm_page_cache(vm_page_t m)
 /*
  * vm_page_advise
  *
- *	Cache, deactivate, or do nothing as appropriate.  This routine
- *	is used by madvise().
- *
- *	Generally speaking we want to move the page into the cache so
- *	it gets reused quickly.  However, this can result in a silly syndrome
- *	due to the page recycling too quickly.  Small objects will not be
- *	fully cached.  On the other hand, if we move the page to the inactive
- *	queue we wind up with a problem whereby very large objects 
- *	unnecessarily blow away our inactive and cache queues.
- *
- *	The solution is to move the pages based on a fixed weighting.  We
- *	either leave them alone, deactivate them, or move them to the cache,
- *	where moving them to the cache has the highest weighting.
- *	By forcing some pages into other queues we eventually force the
- *	system to balance the queues, potentially recovering other unrelated
- *	space from active.  The idea is to not force this to happen too
- *	often.
+ * 	Deactivate or do nothing, as appropriate.  This routine is used
+ * 	by madvise() and vop_stdadvise().
  *
  *	The object and page must be locked.
  */
 void
 vm_page_advise(vm_page_t m, int advice)
 {
-	int dnw, head;
 
 	vm_page_assert_locked(m);
 	VM_OBJECT_ASSERT_WLOCKED(m->object);
-	if (advice == MADV_FREE) {
+	if (advice == MADV_FREE)
 		/*
 		 * Mark the page clean.  This will allow the page to be freed
 		 * up by the system.  However, such pages are often reused
@@ -2656,24 +2647,12 @@ vm_page_advise(vm_page_t m, int advice)
 		 * nor do we try to put it in the cache (which would cause a
 		 * page fault on reuse).
 		 *
-		 * But we do make the page is freeable as we can without
+		 * But we do make the page as freeable as we can without
 		 * actually taking the step of unmapping it.
 		 */
 		m->dirty = 0;
-		m->act_count = 0;
-	} else if (advice != MADV_DONTNEED)
+	else if (advice != MADV_DONTNEED)
 		return;
-	dnw = PCPU_GET(dnweight);
-	PCPU_INC(dnweight);
-
-	/*
-	 * Occasionally leave the page alone.
-	 */
-	if ((dnw & 0x01F0) == 0 || m->queue == PQ_INACTIVE) {
-		if (m->act_count >= ACT_INIT)
-			--m->act_count;
-		return;
-	}
 
 	/*
 	 * Clear any references to the page.  Otherwise, the page daemon will
@@ -2684,20 +2663,12 @@ vm_page_advise(vm_page_t m, int advice)
 	if (advice != MADV_FREE && m->dirty == 0 && pmap_is_modified(m))
 		vm_page_dirty(m);
 
-	if (m->dirty || (dnw & 0x0070) == 0) {
-		/*
-		 * Deactivate the page 3 times out of 32.
-		 */
-		head = 0;
-	} else {
-		/*
-		 * Cache the page 28 times out of every 32.  Note that
-		 * the page is deactivated instead of cached, but placed
-		 * at the head of the queue instead of the tail.
-		 */
-		head = 1;
-	}
-	_vm_page_deactivate(m, head);
+	/*
+	 * Place clean pages at the head of the inactive queue rather than the
+	 * tail, thus defeating the queue's LRU operation and ensuring that the
+	 * page will be reused quickly.
+	 */
+	_vm_page_deactivate(m, m->dirty == 0);
 }
 
 /*
-- 
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