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Date:      Wed, 8 Jul 2015 17:46:00 +0000 (UTC)
From:      Alan Cox <alc@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r285282 - head/sys/vm
Message-ID:  <201507081746.t68Hk0To044278@repo.freebsd.org>
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Author: alc
Date: Wed Jul  8 17:45:59 2015
New Revision: 285282
URL: https://svnweb.freebsd.org/changeset/base/285282

Log:
  The intention of r254304 was to scan the active queue continuously.
  However, I've observed the active queue scan stopping when there are
  frequent free page shortages and the inactive queue is steadily refilled
  by other mechanisms, such as the sequential access heuristic in vm_fault()
  or madvise(2).  To remedy this problem, record the time of the last active
  queue scan, and always scan a number of pages proportional to the time
  since the last scan, regardless of whether that last scan was a
  timeout-triggered ("pass == 0") or free-page-shortage-triggered ("pass >
  0") scan.
  
  Also, on a timeout-triggered scan, allow a full scan of the active queue
  when the system is short of inactive pages.
  
  Reviewed by:	kib
  MFC after:	6 weeks
  Sponsored by:	EMC / Isilon Storage Division

Modified:
  head/sys/vm/vm_page.h
  head/sys/vm/vm_pageout.c

Modified: head/sys/vm/vm_page.h
==============================================================================
--- head/sys/vm/vm_page.h	Wed Jul  8 16:42:28 2015	(r285281)
+++ head/sys/vm/vm_page.h	Wed Jul  8 17:45:59 2015	(r285282)
@@ -227,6 +227,7 @@ struct vm_domain {
 	long vmd_segs;	/* bitmask of the segments */
 	boolean_t vmd_oom;
 	int vmd_pass;	/* local pagedaemon pass */
+	int vmd_last_active_scan;
 	struct vm_page vmd_marker; /* marker for pagedaemon private use */
 };
 

Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c	Wed Jul  8 16:42:28 2015	(r285281)
+++ head/sys/vm/vm_pageout.c	Wed Jul  8 17:45:59 2015	(r285282)
@@ -1028,9 +1028,10 @@ vm_pageout_scan(struct vm_domain *vmd, i
 	vm_page_t m, next;
 	struct vm_pagequeue *pq;
 	vm_object_t object;
+	long min_scan;
 	int act_delta, addl_page_shortage, deficit, maxscan, page_shortage;
 	int vnodes_skipped = 0;
-	int maxlaunder;
+	int maxlaunder, scan_tick, scanned;
 	boolean_t queues_locked;
 
 	/*
@@ -1351,34 +1352,37 @@ relock_queues:
 	 * If we're just idle polling attempt to visit every
 	 * active page within 'update_period' seconds.
 	 */
-	if (pass == 0 && vm_pageout_update_period != 0) {
-		maxscan /= vm_pageout_update_period;
-		page_shortage = maxscan;
-	}
+	scan_tick = ticks;
+	if (vm_pageout_update_period != 0) {
+		min_scan = pq->pq_cnt;
+		min_scan *= scan_tick - vmd->vmd_last_active_scan;
+		min_scan /= hz * vm_pageout_update_period;
+	} else
+		min_scan = 0;
+	if (min_scan > 0 || (page_shortage > 0 && maxscan > 0))
+		vmd->vmd_last_active_scan = scan_tick;
 
 	/*
-	 * Scan the active queue for things we can deactivate. We nominally
-	 * track the per-page activity counter and use it to locate
-	 * deactivation candidates.
-	 */
-	m = TAILQ_FIRST(&pq->pq_pl);
-	while (m != NULL && maxscan-- > 0 && page_shortage > 0) {
+	 * Scan the active queue for pages that can be deactivated.  Update
+	 * the per-page activity counter and use it to identify deactivation
+	 * candidates.
+	 */
+	for (m = TAILQ_FIRST(&pq->pq_pl), scanned = 0; m != NULL && (scanned <
+	    min_scan || (page_shortage > 0 && scanned < maxscan)); m = next,
+	    scanned++) {
 
 		KASSERT(m->queue == PQ_ACTIVE,
 		    ("vm_pageout_scan: page %p isn't active", m));
 
 		next = TAILQ_NEXT(m, plinks.q);
-		if ((m->flags & PG_MARKER) != 0) {
-			m = next;
+		if ((m->flags & PG_MARKER) != 0)
 			continue;
-		}
 		KASSERT((m->flags & PG_FICTITIOUS) == 0,
 		    ("Fictitious page %p cannot be in active queue", m));
 		KASSERT((m->oflags & VPO_UNMANAGED) == 0,
 		    ("Unmanaged page %p cannot be in active queue", m));
 		if (!vm_pageout_page_lock(m, &next)) {
 			vm_page_unlock(m);
-			m = next;
 			continue;
 		}
 
@@ -1430,7 +1434,6 @@ relock_queues:
 		} else
 			vm_page_requeue_locked(m);
 		vm_page_unlock(m);
-		m = next;
 	}
 	vm_pagequeue_unlock(pq);
 #if !defined(NO_SWAPPING)
@@ -1620,6 +1623,7 @@ vm_pageout_worker(void *arg)
 	 */
 
 	KASSERT(domain->vmd_segs != 0, ("domain without segments"));
+	domain->vmd_last_active_scan = ticks;
 	vm_pageout_init_marker(&domain->vmd_marker, PQ_INACTIVE);
 
 	/*

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