svn commit: r337547 - head/sys/vm

[Mark Johnston]

Author: markj
Date: Thu Aug  9 18:25:49 2018
New Revision: 337547
URL: https://svnweb.freebsd.org/changeset/base/337547

Log:
  Account for the lowmem handlers in the inactive queue scan target.
  
  Before r329882 the target would be computed after lowmem handlers run
  and free pages.  On some systems a significant amount of page
  reclamation happens this way.  However, with r329882 the target is
  computed first, which can lead to unnecessary reclamation from the
  page cache, and this in turn may result in excessive swapping.
  
  Instead, adjust the target after running lowmem handlers.  Don't
  invoke the lowmem handlers before the PID controller, though, since
  that would hide the true rate of page allocation.
  
  Reviewed by:	alc, kib (previous version)
  Sponsored by:	The FreeBSD Foundation
  Differential Revision:	https://reviews.freebsd.org/D16606

Modified:
  head/sys/vm/vm_pageout.c

Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c	Thu Aug  9 17:53:18 2018	(r337546)
+++ head/sys/vm/vm_pageout.c	Thu Aug  9 18:25:49 2018	(r337547)
@@ -152,7 +152,6 @@ static int vm_pageout_oom_seq = 12;
 static int vm_pageout_update_period;
 static int disable_swap_pageouts;
 static int lowmem_period = 10;
-static time_t lowmem_uptime;
 static int swapdev_enabled;
 
 static int vm_panic_on_oom = 0;
@@ -1856,12 +1855,17 @@ vm_pageout_oom(int shortage)
 	}
 }
 
-static void
-vm_pageout_lowmem(struct vm_domain *vmd)
+static bool
+vm_pageout_lowmem(void)
 {
+	static int lowmem_ticks = 0;
+	int last;
 
-	if (vmd == VM_DOMAIN(0) &&
-	    time_uptime - lowmem_uptime >= lowmem_period) {
+	last = atomic_load_int(&lowmem_ticks);
+	while ((u_int)(ticks - last) / hz >= lowmem_period) {
+		if (atomic_fcmpset_int(&lowmem_ticks, &last, ticks) == 0)
+			continue;
+
 		/*
 		 * Decrease registered cache sizes.
 		 */
@@ -1873,14 +1877,16 @@ vm_pageout_lowmem(struct vm_domain *vmd)
 		 * drained above.
 		 */
 		uma_reclaim();
-		lowmem_uptime = time_uptime;
+		return (true);
 	}
+	return (false);
 }
 
 static void
 vm_pageout_worker(void *arg)
 {
 	struct vm_domain *vmd;
+	u_int ofree;
 	int addl_shortage, domain, shortage;
 	bool target_met;
 
@@ -1939,11 +1945,16 @@ vm_pageout_worker(void *arg)
 
 		/*
 		 * Use the controller to calculate how many pages to free in
-		 * this interval, and scan the inactive queue.
+		 * this interval, and scan the inactive queue.  If the lowmem
+		 * handlers appear to have freed up some pages, subtract the
+		 * difference from the inactive queue scan target.
 		 */
 		shortage = pidctrl_daemon(&vmd->vmd_pid, vmd->vmd_free_count);
 		if (shortage > 0) {
-			vm_pageout_lowmem(vmd);
+			ofree = vmd->vmd_free_count;
+			if (vm_pageout_lowmem() && vmd->vmd_free_count > ofree)
+				shortage -= min(vmd->vmd_free_count - ofree,
+				    (u_int)shortage);
 			target_met = vm_pageout_scan_inactive(vmd, shortage,
 			    &addl_shortage);
 		} else