3805 arc shouldn't cache freed blocks

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Richard Elling <richard.elling@dey-sys.com>
Reviewed by: Will Andrews <will@firepipe.net>
Approved by: Dan McDonald <danmcd@nexenta.com>

usr/src/uts/common/fs/zfs/arc.c

@@ -3110,6 +3110,34 @@ arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private)
 	buf->b_private = private;
 }
 
+/*
+ * Notify the arc that a block was freed, and thus will never be used again.
+ */
+void
+arc_freed(spa_t *spa, const blkptr_t *bp)
+{
+	arc_buf_hdr_t *hdr;
+	kmutex_t *hash_lock;
+	uint64_t guid = spa_load_guid(spa);
+
+	hdr = buf_hash_find(guid, BP_IDENTITY(bp), BP_PHYSICAL_BIRTH(bp),
+	    &hash_lock);
+	if (hdr == NULL)
+		return;
+	if (HDR_BUF_AVAILABLE(hdr)) {
+		arc_buf_t *buf = hdr->b_buf;
+		add_reference(hdr, hash_lock, FTAG);
+		hdr->b_flags &= ~ARC_BUF_AVAILABLE;
+		mutex_exit(hash_lock);
+
+		arc_release(buf, FTAG);
+		(void) arc_buf_remove_ref(buf, FTAG);
+	} else {
+		mutex_exit(hash_lock);
+	}
+
+}
+
 /*
  * This is used by the DMU to let the ARC know that a buffer is
  * being evicted, so the ARC should clean up.  If this arc buf

usr/src/uts/common/fs/zfs/sys/arc.h

@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012 by Delphix. All rights reserved.
+ * Copyright (c) 2013 by Delphix. All rights reserved.
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  */
 
@@ -110,6 +110,7 @@ zio_t *arc_write(zio_t *pio, spa_t *spa, uint64_t txg,
     blkptr_t *bp, arc_buf_t *buf, boolean_t l2arc, boolean_t l2arc_compress,
     const zio_prop_t *zp, arc_done_func_t *ready, arc_done_func_t *done,
     void *private, int priority, int zio_flags, const zbookmark_t *zb);
+void arc_freed(spa_t *spa, const blkptr_t *bp);
 
 void arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private);
 int arc_buf_evict(arc_buf_t *buf);

usr/src/uts/common/fs/zfs/zio.c

@@ -715,6 +715,7 @@ zio_free_sync(zio_t *pio, spa_t *spa, uint64_t txg, const blkptr_t *bp,
 	ASSERT(spa_sync_pass(spa) < zfs_sync_pass_deferred_free);
 
 	metaslab_check_free(spa, bp);
+	arc_freed(spa, bp);
 
 	zio = zio_create(pio, spa, txg, bp, NULL, BP_GET_PSIZE(bp),
 	    NULL, NULL, ZIO_TYPE_FREE, ZIO_PRIORITY_FREE, flags,