kernel - Add vm.swapcache.maxscan

* Add vm.swapcache.maxscan as a separate counter from vm.swapcache.maxlaunder.

* Defaults to 4x maxlaunder.

* Should hopefully fix another cpu hogging issue that was noticed on
  avalon when most VM pages wind up being cached in the swapcache
  but still get cycled in the PQ_INACTIVE VM page queue due to apache
  activity.

diff --git a/sys/vm/vm_swapcache.c b/sys/vm/vm_swapcache.c
index 38aaf9b..638857a 100644 (file)
--- a/sys/vm/vm_swapcache.c
+++ b/sys/vm/vm_swapcache.c
@@ -92,6 +92,7 @@ SYSCTL_NODE(_vm, OID_AUTO, swapcache, CTLFLAG_RW, NULL, NULL);
 int vm_swapcache_read_enable;
 int vm_swapcache_inactive_heuristic;
 static int vm_swapcache_sleep;
+static int vm_swapcache_maxscan = 256 * 4;
 static int vm_swapcache_maxlaunder = 256;
 static int vm_swapcache_data_enable = 0;
 static int vm_swapcache_meta_enable = 0;
@@ -108,6 +109,8 @@ static int64_t vm_swapcache_cleanperobj = 16*1024*1024;
 
 SYSCTL_INT(_vm_swapcache, OID_AUTO, maxlaunder,
        CTLFLAG_RW, &vm_swapcache_maxlaunder, 0, "");
+SYSCTL_INT(_vm_swapcache, OID_AUTO, maxscan,
+       CTLFLAG_RW, &vm_swapcache_maxscan, 0, "");
 
 SYSCTL_INT(_vm_swapcache, OID_AUTO, data_enable,
        CTLFLAG_RW, &vm_swapcache_data_enable, 0, "");
@@ -308,6 +311,7 @@ vm_swapcache_writing(vm_page_t marker)
        struct vnode *vp;
        vm_page_t m;
        int count;
+       int scount;
        int isblkdev;
 
        /*
@@ -329,16 +333,13 @@ vm_swapcache_writing(vm_page_t marker)
         * suitable pages to push to the swap cache.
         *
         * We are looking for clean vnode-backed pages.
-        *
-        * NOTE: PG_SWAPPED pages in particular are not part of
-        *       our count because once the cache stabilizes we
-        *       can end up with a very high datarate of VM pages
-        *       cycling from it.
         */
        count = vm_swapcache_maxlaunder;
+       scount = vm_swapcache_maxscan;
 
        vm_page_queues_spin_lock(marker->queue);
-       while ((m = TAILQ_NEXT(marker, pageq)) != NULL && count-- > 0) {
+       while ((m = TAILQ_NEXT(marker, pageq)) != NULL &&
+              count > 0 && scount-- > 0) {
                KKASSERT(m->queue == marker->queue);
 
                if (vm_swapcache_curburst < 0)
@@ -352,10 +353,8 @@ vm_swapcache_writing(vm_page_t marker)
                 * Ignore markers and ignore pages that already have a swap
                 * assignment.
                 */
-               if (m->flags & (PG_MARKER | PG_SWAPPED)) {
-                       ++count;
+               if (m->flags & (PG_MARKER | PG_SWAPPED))
                        continue;
-               }
                if (vm_page_busy_try(m, TRUE))
                        continue;
                vm_page_queues_spin_unlock(marker->queue);
@@ -459,7 +458,7 @@ vm_swapcache_writing(vm_page_t marker)
                 *
                 * (adjust for the --count which also occurs in the loop)
                 */
-               count -= vm_swapcached_flush(m, isblkdev) - 1;
+               count -= vm_swapcached_flush(m, isblkdev);
 
                /*
                 * Setup for next loop using marker.
@@ -636,9 +635,11 @@ vm_swapcache_cleaning(vm_object_t marker)
        vm_object_t object;
        struct vnode *vp;
        int count;
+       int scount;
        int n;
 
        count = vm_swapcache_maxlaunder;
+       scount = vm_swapcache_maxscan;
 
        /*
         * Look for vnode objects
@@ -659,7 +660,7 @@ vm_swapcache_cleaning(vm_object_t marker)
                 * Safety, or in case there are millions of VM objects
                 * without swapcache backing.
                 */
-               if (--count <= 0)
+               if (--scount <= 0)
                        break;
 
                /*