Author: markj
Date: Thu May 24 20:26:37 2018
New Revision: 334179
URL: https://svnweb.freebsd.org/changeset/base/334179
Log:
Update r334154 with review feedback from D15490.
An old revision was committed by accident.
Differential Revision: https://reviews.freebsd.org/D15490
Modified:
head/sys/vm/vm_pageout.c
Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c Thu May 24 18:53:29 2018 (r334178)
+++ head/sys/vm/vm_pageout.c Thu May 24 20:26:37 2018 (r334179)
@@ -1111,16 +1111,16 @@ dolaundry:
* Compute the number of pages we want to try to move from the
* active queue to either the inactive or laundry queue.
*
- * When scanning active pages, we make clean pages count more heavily
- * towards the page shortage than dirty pages. This is because dirty
- * pages must be laundered before they can be reused and thus have less
- * utility when attempting to quickly alleviate a shortage. However,
- * this weighting also causes the scan to deactivate dirty pages more
- * aggressively, improving the effectiveness of clustering and
- * ensuring that they can eventually be reused.
+ * When scanning active pages during a shortage, we make clean pages
+ * count more heavily towards the page shortage than dirty pages.
+ * This is because dirty pages must be laundered before they can be
+ * reused and thus have less utility when attempting to quickly
+ * alleviate a free page shortage. However, this weighting also
+ * causes the scan to deactivate dirty pages more aggressively,
+ * improving the effectiveness of clustering.
*/
static int
-vm_pageout_scan_active_target(struct vm_domain *vmd)
+vm_pageout_active_target(struct vm_domain *vmd)
{
int shortage;
@@ -1169,12 +1169,12 @@ vm_pageout_scan_active(struct vm_domain *vmd, int page
* candidates. Held pages may be deactivated.
*
* To avoid requeuing each page that remains in the active queue, we
- * implement the CLOCK algorithm. To maintain consistency in the
- * generic page queue code, pages are inserted at the tail of the
- * active queue. We thus use two hands, represented by marker pages:
- * scans begin at the first hand, which precedes the second hand in
- * the queue. When the two hands meet, they are moved back to the
- * head and tail of the queue, respectively, and scanning resumes.
+ * implement the CLOCK algorithm. To keep the implementation of the
+ * enqueue operation consistent for all page queues, we use two hands,
+ * represented by marker pages. Scans begin at the first hand, which
+ * precedes the second hand in the queue. When the two hands meet,
+ * they are moved back to the head and tail of the queue, respectively,
+ * and scanning resumes.
*/
max_scan = page_shortage > 0 ? pq->pq_cnt : min_scan;
mtx = NULL;
@@ -1254,9 +1254,12 @@ act_scan:
* through the inactive queue before moving to the
* laundry queues. This gives them some extra time to
* be reactivated, potentially avoiding an expensive
- * pageout. During a page shortage, the inactive queue
- * is necessarily small, so we may move dirty pages
- * directly to the laundry queue.
+ * pageout. However, during a page shortage, the
+ * inactive queue is necessarily small, and so dirty
+ * pages would only spend a trivial amount of time in
+ * the inactive queue. Therefore, we might as well
+ * place them directly in the laundry queue to reduce
+ * queuing overhead.
*/
if (page_shortage <= 0)
vm_page_deactivate(m);
@@ -1941,7 +1944,7 @@ vm_pageout_worker(void *arg)
* indicates that we must aggressively deactivate pages to avoid
* a shortfall.
*/
- shortage = vm_pageout_scan_active_target(vmd) + addl_shortage;
+ shortage = vm_pageout_active_target(vmd) + addl_shortage;
vm_pageout_scan_active(vmd, shortage);
/*