Micro-optimize free_pv_entry() for the expected case.

1 files changed, 6 insertions, 4 deletions

diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index f293aaf1c251..ff4f96ba330f 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -2095,7 +2095,6 @@ pmap_collect(pmap_t locked_pmap, struct vpgqueues *vpq)
 	}
 }
 
-
 /*
  * free the pv_entry back to the free list
  */
@@ -2116,13 +2115,16 @@ free_pv_entry(pmap_t pmap, pv_entry_t pv)
 	field = idx / 64;
 	bit = idx % 64;
 	pc->pc_map[field] |= 1ul << bit;
-	/* move to head of list */
-	TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list);
 	if (pc->pc_map[0] != PC_FREE0 || pc->pc_map[1] != PC_FREE1 ||
 	    pc->pc_map[2] != PC_FREE2) {
-		TAILQ_INSERT_HEAD(&pmap->pm_pvchunk, pc, pc_list);
+		/* 98% of the time, pc is already at the head of the list. */
+		if (__predict_false(pc != TAILQ_FIRST(&pmap->pm_pvchunk))) {
+			TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list);
+			TAILQ_INSERT_HEAD(&pmap->pm_pvchunk, pc, pc_list);
+		}
 		return;
 	}
+	TAILQ_REMOVE(&pmap->pm_pvchunk, pc, pc_list);
 	PV_STAT(pv_entry_spare -= _NPCPV);
 	PV_STAT(pc_chunk_count--);
 	PV_STAT(pc_chunk_frees++);