OpenZFS 9321 - arc_loan_compressed_buf() can increment arc_loaned_byt…

…es by the wrong value

Authored by: Allan Jude <allanjude@freebsd.org>
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Garrett D'Amore <garrett@damore.org>
Ported-by: Giuseppe Di Natale <dinatale2@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/9321
OpenZFS-commit: openzfs/openzfs@92b05f3a18
Closes #7333

module/zfs/arc.c

@@ -2919,7 +2919,7 @@ arc_loan_buf(spa_t *spa, boolean_t is_metadata, int size)
 	arc_buf_t *buf = arc_alloc_buf(spa, arc_onloan_tag,
 	    is_metadata ? ARC_BUFC_METADATA : ARC_BUFC_DATA, size);
 
-	arc_loaned_bytes_update(size);
+	arc_loaned_bytes_update(arc_buf_size(buf));
 
 	return (buf);
 }
@@ -2931,7 +2931,7 @@ arc_loan_compressed_buf(spa_t *spa, uint64_t psize, uint64_t lsize,
 	arc_buf_t *buf = arc_alloc_compressed_buf(spa, arc_onloan_tag,
 	    psize, lsize, compression_type);
 
-	arc_loaned_bytes_update(psize);
+	arc_loaned_bytes_update(arc_buf_size(buf));
 
 	return (buf);
 }