svn commit: r361965 - head/sys/vm

[Mateusz Guzik]

Author: mjg
Date: Tue Jun  9 14:16:18 2020
New Revision: 361965
URL: https://svnweb.freebsd.org/changeset/base/361965

Log:
  vm: rework swap_pager_status to execute in constant time
  
  The lock-protected iteration is trivially avoidable.
  
  This removes a serialisation point from Linux binaries (which end up calling
  here from the sysinfo syscall).

Modified:
  head/sys/vm/swap_pager.c

Modified: head/sys/vm/swap_pager.c
==============================================================================
--- head/sys/vm/swap_pager.c	Tue Jun  9 09:42:39 2020	(r361964)
+++ head/sys/vm/swap_pager.c	Tue Jun  9 14:16:18 2020	(r361965)
@@ -2541,16 +2541,10 @@ swapoff_all(void)
 void
 swap_pager_status(int *total, int *used)
 {
-	struct swdevt *sp;
 
-	*total = 0;
-	*used = 0;
-	mtx_lock(&sw_dev_mtx);
-	TAILQ_FOREACH(sp, &swtailq, sw_list) {
-		*total += sp->sw_nblks;
-		*used += sp->sw_used;
-	}
-	mtx_unlock(&sw_dev_mtx);
+	*total = swap_total;
+	*used = swap_total - swap_pager_avail -
+	    nswapdev * howmany(BBSIZE, PAGE_SIZE);
 }
 
 int