From: Ying Zhu <casualfisher@gmail.com>
Date: Sat, 29 Jun 2013 07:03:49 +0000 (+0800)
Subject: Improve code in arc_buf_remove_ref
X-Git-Url: https://git.camperquake.de/gitweb.cgi?p=zfs.git;a=commitdiff_plain;h=b4f7f105275d996fbcb6abd65760307d2153a89b

Improve code in arc_buf_remove_ref

When we remove references of arc bufs in the arc_anon state we
needn't take its header's hash_lock, so postpone it to where we
really need it to avoid unnecessary invocations of function buf_hash.

Signed-off-by: Ying Zhu <casualfisher@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1557
---

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index de86966..df3aeb7 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -1642,7 +1642,7 @@ int
 arc_buf_remove_ref(arc_buf_t *buf, void* tag)
 {
 	arc_buf_hdr_t *hdr = buf->b_hdr;
-	kmutex_t *hash_lock = HDR_LOCK(hdr);
+	kmutex_t *hash_lock = NULL;
 	int no_callback = (buf->b_efunc == NULL);
 
 	if (hdr->b_state == arc_anon) {
@@ -1651,6 +1651,7 @@ arc_buf_remove_ref(arc_buf_t *buf, void* tag)
 		return (no_callback);
 	}
 
+	hash_lock = HDR_LOCK(hdr);
 	mutex_enter(hash_lock);
 	hdr = buf->b_hdr;
 	ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));