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Date:      Sun, 12 Jan 2014 19:04:21 +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: r260567 - head/sys/vm
Message-ID:  <201401121904.s0CJ4LnM063570@svn.freebsd.org>
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Author: alc
Date: Sun Jan 12 19:04:20 2014
New Revision: 260567
URL: http://svnweb.freebsd.org/changeset/base/260567

Log:
  Correctly update the count of stuck pages, "addl_page_shortage", in
  vm_pageout_scan().  There were missing increments in two less common cases.
  
  Don't conflate the count of stuck pages and the pageout deficit provided by
  vm_page_alloc{,_contig}().  (A proposed fix to the OOM code depends on this.)
  
  Handle held pages consistently in the inactive queue scan.  In the more
  common case, we did not move the page to the tail of the queue.  Whereas, in
  the less common case, we did.  There's no particular reason to move the page
  in the less common case, so remove it.
  
  Perform the calculation of the page shortage for the active queue scan a
  little earlier, before the active queue lock is acquired.  The correctness
  of this calculation doesn't depend on the active queue lock being held.
  
  Eliminate a redundant variable, "pcount".  Use the more descriptive
  variable, "maxscan", in its place.
  
  Apply a few nearby style fixes, e.g., eliminate stray whitespace and excess
  parentheses.
  
  Reviewed by:	kib
  Sponsored by:	EMC / Isilon Storage Division

Modified:
  head/sys/vm/vm_pageout.c

Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c	Sun Jan 12 17:40:47 2014	(r260566)
+++ head/sys/vm/vm_pageout.c	Sun Jan 12 19:04:20 2014	(r260567)
@@ -909,10 +909,8 @@ vm_pageout_scan(struct vm_domain *vmd, i
 {
 	vm_page_t m, next;
 	struct vm_pagequeue *pq;
-	int page_shortage, maxscan, pcount;
-	int addl_page_shortage;
 	vm_object_t object;
-	int act_delta;
+	int act_delta, addl_page_shortage, deficit, maxscan, page_shortage;
 	int vnodes_skipped = 0;
 	int maxlaunder;
 	int lockmode;
@@ -942,13 +940,15 @@ vm_pageout_scan(struct vm_domain *vmd, i
 	 * number of pages from the inactive count that should be
 	 * discounted in setting the target for the active queue scan.
 	 */
-	addl_page_shortage = atomic_readandclear_int(&vm_pageout_deficit);
+	addl_page_shortage = 0;
+
+	deficit = atomic_readandclear_int(&vm_pageout_deficit);
 
 	/*
 	 * Calculate the number of pages we want to either free or move
 	 * to the cache.
 	 */
-	page_shortage = vm_paging_target() + addl_page_shortage;
+	page_shortage = vm_paging_target() + deficit;
 
 	/*
 	 * maxlaunder limits the number of dirty pages we flush per scan.
@@ -1245,6 +1245,7 @@ vm_pageout_scan(struct vm_domain *vmd, i
 				 */
 				if (vm_page_busied(m)) {
 					vm_page_unlock(m);
+					addl_page_shortage++;
 					goto unlock_and_continue;
 				}
 
@@ -1252,9 +1253,9 @@ vm_pageout_scan(struct vm_domain *vmd, i
 				 * If the page has become held it might
 				 * be undergoing I/O, so skip it
 				 */
-				if (m->hold_count) {
+				if (m->hold_count != 0) {
 					vm_page_unlock(m);
-					vm_page_requeue_locked(m);
+					addl_page_shortage++;
 					if (object->flags & OBJ_MIGHTBEDIRTY)
 						vnodes_skipped++;
 					goto unlock_and_continue;
@@ -1309,19 +1310,20 @@ relock_queues:
 	 * Compute the number of pages we want to try to move from the
 	 * active queue to the inactive queue.
 	 */
+	page_shortage = cnt.v_inactive_target - cnt.v_inactive_count +
+	    vm_paging_target() + deficit + addl_page_shortage;
+
 	pq = &vmd->vmd_pagequeues[PQ_ACTIVE];
 	vm_pagequeue_lock(pq);
-	pcount = pq->pq_cnt;
-	page_shortage = vm_paging_target() +
-	    cnt.v_inactive_target - cnt.v_inactive_count;
-	page_shortage += addl_page_shortage;
+	maxscan = pq->pq_cnt;
+
 	/*
 	 * If we're just idle polling attempt to visit every
 	 * active page within 'update_period' seconds.
 	 */
-	 if (pass == 0 && vm_pageout_update_period != 0) {
-		pcount /= vm_pageout_update_period;
-		page_shortage = pcount;
+	if (pass == 0 && vm_pageout_update_period != 0) {
+		maxscan /= vm_pageout_update_period;
+		page_shortage = maxscan;
 	}
 
 	/*
@@ -1330,7 +1332,7 @@ relock_queues:
 	 * deactivation candidates.
 	 */
 	m = TAILQ_FIRST(&pq->pq_pl);
-	while ((m != NULL) && (pcount-- > 0) && (page_shortage > 0)) {
+	while (m != NULL && maxscan-- > 0 && page_shortage > 0) {
 
 		KASSERT(m->queue == PQ_ACTIVE,
 		    ("vm_pageout_scan: page %p isn't active", m));

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