From: Ronnie Sahlberg <lsahlber@redhat.com>
To: linux-cifs <linux-cifs@vger.kernel.org>
Cc: Steve French <smfrench@gmail.com>,
Pavel Shilovsky <pshilov@microsoft.com>,
Ronnie Sahlberg <lsahlber@redhat.com>
Subject: [PATCH 4/6] cifs: prevent starvation in wait_for_free_credits for multi-credit requests
Date: Wed, 6 Mar 2019 14:15:44 +1000 [thread overview]
Message-ID: <20190306041546.10419-5-lsahlber@redhat.com> (raw)
In-Reply-To: <20190306041546.10419-1-lsahlber@redhat.com>
Reserve the last MAX_COMPOUND credits for any request asking for >1 credit.
This is to prevent future compound requests from becoming starved while waiting
for potentially many requests is there is a large number of concurrent
singe-credit requests.
However, we need to protect from servers that are very slow to hand out
new credits on new sessions so we only do this IFF there are 2*MAX_COMPOUND
(arbitrary) credits already in flight.
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
fs/cifs/transport.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index baf15194aa3d..f4ec9635dab2 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -520,6 +520,34 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
}
/*
+ * For normal commands, reserve the last MAX_COMPOUND
+ * credits to compound requests.
+ * Otherwise these compounds could be permanently
+ * starved for credits by single-credit requests.
+ *
+ * To prevent spinning CPU, block this thread until
+ * there are >MAX_COMPOUND credits available.
+ * But only do this is we already have a lot of
+ * credits in flight to avoid triggering this check
+ * for servers that are slow to hand out credits on
+ * new sessions.
+ */
+ if (!optype && num_credits == 1 &&
+ server->in_flight > 2 * MAX_COMPOUND &&
+ *credits <= MAX_COMPOUND) {
+ spin_unlock(&server->req_lock);
+ cifs_num_waiters_inc(server);
+ rc = wait_event_killable(server->request_q,
+ has_credits(server, credits,
+ MAX_COMPOUND + 1));
+ cifs_num_waiters_dec(server);
+ if (rc)
+ return rc;
+ spin_lock(&server->req_lock);
+ continue;
+ }
+
+ /*
* Can not count locking commands against total
* as they are allowed to block on server.
*/
--
2.13.6
next prev parent reply other threads:[~2019-03-06 4:16 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-06 4:15 [PATCH 0/6] cifs: simplify handling of credits for compounds Ronnie Sahlberg
2019-03-06 4:15 ` [PATCH 1/6] cifs: change wait_for_free_request() to take flags as argument Ronnie Sahlberg
2019-03-06 4:15 ` [PATCH 2/6] cifs: pass flags down into wait_for_free_credits() Ronnie Sahlberg
2019-03-06 4:15 ` [PATCH 3/6] cifs: wait_for_free_credits() make it possible to wait for >=1 credits Ronnie Sahlberg
2019-03-06 4:15 ` Ronnie Sahlberg [this message]
2019-03-06 4:15 ` [PATCH 5/6] cifs: add a timeout argument to wait_for_free_credits Ronnie Sahlberg
2019-03-06 17:32 ` Pavel Shilovsky
2019-03-08 2:39 ` ronnie sahlberg
2019-03-06 4:15 ` [PATCH 6/6] cifs: simplify how we handle credits in compond_send_recv() Ronnie Sahlberg
2019-03-06 17:26 ` Pavel Shilovsky
2019-03-08 2:58 [PATCH 0/6] cifs: simplify handling of credits for compounds Ronnie Sahlberg
2019-03-08 2:58 ` [PATCH 4/6] cifs: prevent starvation in wait_for_free_credits for multi-credit requests Ronnie Sahlberg
2019-03-09 0:55 ` Pavel Shilovsky
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