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Re: [dm-devel] Re: DM configuration



Hi,

On Wed, 5 Oct 2005 15:45:05 +0200, Christophe Varoqui <christophe varoqui free fr> wrote:
> > 1) Under all path failure condition or the device is removed from array
> > (using management station), IO continues if "queue_if_no_path" feature
> > is enabled. As all the requests are cached all the memory gets used out
> > for this. Can there be any mechanism where the all path failure is
> > detected and marked, devices can be suspended or removed after some time
> > (user configurable). By doing this the OS stalling can be avoided when
> > the LUN is in dead state for prolonged period of time.
> > 
> Wouldn't it be adequate to solve this issue in the queue_if_no_path
> limiting framework that should be worked on (time-based, queue depth-based,
> both, ...?)
> 
> After all, the admin should "multipath -f $sssu_wants_to_kill_me") before,
> shouldn't it ? Think of mounted FS, for example ... the admin *has* to
> do something on the system anyway.

Indeed.
But I think that taking care of that in multipathd is also needed.
While kernel space solution may be better to solve daemon crash
issue and so on, user space solution will keep the kernel code simple,
as discussed in the following thread.

  Subject: [dm-devel] queue_if_no_paths timeout handling
  URL    : https://www.redhat.com/archives/dm-devel/2005-July/msg00035.html

The following patch adds time-based retry feature in no-path situation
to multipathd.  Any comments are welcome.


This patch adds 'no_path_retry' option to multipathd.

   o no_path_retry = "fail" is equal to 'fail_if_no_path'.
     (i.e. I/O to the no-path map will immediately fail.)

   o no_path_retry = "queue" is equal to 'queue_if_no_path'.
     (i.e. I/O to the no-path map will be queued until any path comes up.)

   o If no_path_retry = <n> where n is positive number,
     then multipathd will set queue_if_no_path to the map,
     and if the all paths are down, multipathd will turn the feature
     off to fail_if_no_path after the checker tries <n> times for each
     paths in the map.

Multipathd re-writes queue_if_no_path feature parameter in the map,
if this option is specified.  But by default, this patch doesn't
change current multipathd behaviour.
So this patch don't break any existing configuration.

# Multipathd has "features" option, with which user can directly specify
# a feature parameter of the table (e.g. features="1 queue_if_no_path").
# However, no_path_retry could be considered as smarter replacement for it.


diff -rup git/libmultipath/config.h retry-multipathd/libmultipath/config.h
--- git/libmultipath/config.h	2005-09-28 12:32:02.000000000 -0400
+++ retry-multipathd/libmultipath/config.h	2005-10-05 18:37:33.000000000 -0400
@@ -33,6 +33,7 @@ struct mpentry {
 	int pgpolicy;
 	int pgfailback;
 	int rr_weight;
+	int no_path_retry;
 
 	char * wwid;
 	char * selector;
@@ -56,6 +57,7 @@ struct config {
 	int pgfailback;
 	int remove;
 	int rr_weight;
+	int default_no_path_retry;
 
 	char * dev;
 	char * udev_dir;
diff -rup git/libmultipath/devmapper.c retry-multipathd/libmultipath/devmapper.c
--- git/libmultipath/devmapper.c	2005-10-04 12:20:03.000000000 -0400
+++ retry-multipathd/libmultipath/devmapper.c	2005-10-05 18:39:36.000000000 -0400
@@ -490,6 +490,41 @@ out:
 	return r;
 }
 
+int
+dm_queue_if_no_path(char *mapname, int enable)
+{
+	int r = 1;
+	struct dm_task *dmt;
+	char *str;
+
+	if (enable)
+		str = "queue_if_no_path\n";
+	else
+		str = "fail_if_no_path\n";
+
+	if (!(dmt = dm_task_create(DM_DEVICE_TARGET_MSG)))
+		return 1;
+
+	if (!dm_task_set_name(dmt, mapname))
+		goto out;
+
+	if (!dm_task_set_sector(dmt, 0))
+		goto out;
+
+	if (!dm_task_set_message(dmt, str))
+		goto out;
+
+	dm_task_no_open_count(dmt);
+
+	if (!dm_task_run(dmt))
+		goto out;
+
+	r = 0;
+out:
+	dm_task_destroy(dmt);
+	return r;
+}
+
 static int
 dm_groupmsg (char * msg, char * mapname, int index)
 {
diff -rup git/libmultipath/devmapper.h retry-multipathd/libmultipath/devmapper.h
--- git/libmultipath/devmapper.h	2005-09-30 14:13:49.000000000 -0400
+++ retry-multipathd/libmultipath/devmapper.h	2005-10-05 18:39:58.000000000 -0400
@@ -10,6 +10,7 @@ int dm_flush_map (char *, char *);
 int dm_flush_maps (char *);
 int dm_fail_path(char * mapname, char * path);
 int dm_reinstate(char * mapname, char * path);
+int dm_queue_if_no_path(char *mapname, int enable);
 int dm_switchgroup(char * mapname, int index);
 int dm_enablegroup(char * mapname, int index);
 int dm_disablegroup(char * mapname, int index);
diff -rup git/libmultipath/dict.c retry-multipathd/libmultipath/dict.c
--- git/libmultipath/dict.c	2005-09-28 12:32:02.000000000 -0400
+++ retry-multipathd/libmultipath/dict.c	2005-10-05 18:43:51.000000000 -0400
@@ -171,6 +171,26 @@ default_failback_handler(vector strvec)
 	return 0;
 }
 
+static int
+def_no_path_retry_handler(vector strvec)
+{
+	char * buff;
+
+	buff = set_value(strvec);
+	if (!buff)
+		return 1;
+
+	if (!strncmp(buff, "fail", 4) || !strncmp(buff, "0", 1))
+		conf->default_no_path_retry = NO_PATH_RETRY_FAIL;
+	else if (!strncmp(buff, "queue", 5))
+		conf->default_no_path_retry = NO_PATH_RETRY_QUEUE;
+	else if ((conf->default_no_path_retry = atoi(buff)) < 1)
+		conf->default_no_path_retry = NO_PATH_RETRY_UNDEF;
+
+	FREE(buff);
+	return 0;
+}
+
 /*
  * blacklist block handlers
  */
@@ -579,6 +599,30 @@ mp_weight_handler(vector strvec)
 	return 0;
 }
 
+static int
+mp_no_path_retry_handler(vector strvec)
+{
+	struct mpentry *mpe = VECTOR_LAST_SLOT(conf->mptable);
+	char *buff;
+
+	if (!mpe)
+		return 1;
+
+	buff = set_value(strvec);
+	if (!buff)
+		return 1;
+
+	if (!strncmp(buff, "fail", 4) || !strncmp(buff, "0", 1))
+		mpe->no_path_retry = NO_PATH_RETRY_FAIL;
+	else if (!strncmp(buff, "queue", 5))
+		mpe->no_path_retry = NO_PATH_RETRY_QUEUE;
+	else if ((mpe->no_path_retry = atoi(buff)) < 1)
+		mpe->no_path_retry = NO_PATH_RETRY_UNDEF;
+
+	FREE(buff);
+	return 0;
+}
+
 vector
 init_keywords(void)
 {
@@ -596,6 +640,7 @@ init_keywords(void)
 	install_keyword("failback", &default_failback_handler);
 	install_keyword("rr_min_io", &def_minio_handler);
 	install_keyword("rr_weight", &def_weight_handler);
+	install_keyword("default_no_path_retry", &def_no_path_retry_handler);
 	
 	install_keyword_root("devnode_blacklist", &blacklist_handler);
 	install_keyword("devnode", &ble_handler);
@@ -626,6 +671,7 @@ init_keywords(void)
 	install_keyword("path_selector", &mp_selector_handler);
 	install_keyword("failback", &mp_failback_handler);
 	install_keyword("rr_weight", &mp_weight_handler);
+	install_keyword("no_path_retry", &mp_no_path_retry_handler);
 	install_sublevel_end();
 
 	return keywords;
diff -rup git/libmultipath/propsel.c retry-multipathd/libmultipath/propsel.c
--- git/libmultipath/propsel.c	2005-09-28 12:32:02.000000000 -0400
+++ retry-multipathd/libmultipath/propsel.c	2005-10-05 18:46:03.000000000 -0400
@@ -201,3 +201,22 @@ select_getprio (struct path * pp)
 	return 0;
 }
 
+extern int
+select_no_path_retry(struct multipath *mp)
+{
+	if (mp->mpe && mp->mpe->no_path_retry != NO_PATH_RETRY_UNDEF) {
+		mp->no_path_retry = mp->mpe->no_path_retry;
+		condlog(3, "no_path_retry = %i (controler setting)",
+			mp->no_path_retry);
+		return 0;
+	}
+	if (conf->default_no_path_retry != NO_PATH_RETRY_UNDEF) {
+		mp->no_path_retry = conf->default_no_path_retry;
+		condlog(3, "no_path_retry = %i (config file default)",
+			mp->no_path_retry);
+		return 0;
+	}
+	mp->no_path_retry = NO_PATH_RETRY_UNDEF;
+	condlog(3, "no_path_retry = NONE (internal default)");
+	return 0;
+}
diff -rup git/libmultipath/propsel.h retry-multipathd/libmultipath/propsel.h
--- git/libmultipath/propsel.h	2005-08-29 09:41:06.000000000 -0400
+++ retry-multipathd/libmultipath/propsel.h	2005-10-05 18:46:21.000000000 -0400
@@ -8,4 +8,4 @@ int select_hwhandler (struct multipath *
 int select_checkfn(struct path *pp);
 int select_getuid (struct path * pp);
 int select_getprio (struct path * pp);
-
+int select_no_path_retry(struct multipath *mp);
diff -rup git/libmultipath/structs.h retry-multipathd/libmultipath/structs.h
--- git/libmultipath/structs.h	2005-10-04 12:20:03.000000000 -0400
+++ retry-multipathd/libmultipath/structs.h	2005-10-05 18:51:01.000000000 -0400
@@ -14,6 +14,10 @@
 #define SCSI_PRODUCT_SIZE	17
 #define SCSI_REV_SIZE		5
 
+#define NO_PATH_RETRY_UNDEF	0
+#define NO_PATH_RETRY_FAIL	-1
+#define NO_PATH_RETRY_QUEUE	-2
+
 enum free_path_switch {
 	KEEP_PATHS,
 	FREE_PATHS
@@ -115,6 +119,9 @@ struct multipath {
 	int pgfailback;
 	int failback_tick;
 	int rr_weight;
+	int nr_active;     /* current available(= not known as failed) paths */
+	int no_path_retry; /* number of retries after all paths are down */
+	int retry_tick;    /* remaining times for retries */
 	unsigned long long size;
 	vector paths;
 	vector pg;
diff -rup git/multipath.conf.annotated retry-multipathd/multipath.conf.annotated
--- git/multipath.conf.annotated	2005-09-28 12:32:02.000000000 -0400
+++ retry-multipathd/multipath.conf.annotated	2005-10-05 18:53:28.000000000 -0400
@@ -99,6 +99,17 @@
 #	# default : immediate
 #	#
 #	failback	manual
+#
+#	#
+#	# name    : default_no_path_retry
+#	# scope   : multipathd
+#	# desc    : tell the number of retries until disable queueing, or
+#	#           "fail" means immediate failure (no queueing),
+#	#           "queue" means never stop queueing
+#	# values  : queue|fail|n (>0)
+#	# default : (null)
+#	#
+#	#default_no_path_retry  queue
 #}
 #	
 ##
@@ -177,6 +188,17 @@
 #		# default : immediate
 #		#
 #		failback		manual
+#
+#		#
+#		# name    : no_path_retry
+#		# scope   : multipathd
+#		# desc    : tell the number of retries until disable queueing, or
+#		#           "fail" means immediate failure (no queueing),
+#		#           "queue" means never stop queueing
+#		# values  : queue|fail|n (>0)
+#		# default : (null)
+#		#
+#		#no_path_retry  queue
 #	}
 #	multipath {
 #		wwid	1DEC_____321816758474
diff -rup git/multipathd/main.c retry-multipathd/multipathd/main.c
--- git/multipathd/main.c	2005-09-28 12:32:02.000000000 -0400
+++ retry-multipathd/multipathd/main.c	2005-10-06 11:48:47.000000000 -0400
@@ -209,6 +209,21 @@ set_multipath_wwid (struct multipath * m
 }
 
 static int
+pathcount (struct multipath *mpp, int state)
+{
+	struct pathgroup *pgp;
+	struct path *pp;
+	int i, j;
+	int count = 0;
+
+	vector_foreach_slot (mpp->pg, pgp, i)
+		vector_foreach_slot (pgp->paths, pp, j)
+			if (pp->state == state)
+				count++;
+	return count;
+}
+
+static int
 setup_multipath (struct vectors * vecs, struct multipath * mpp)
 {
 	int i;
@@ -222,6 +237,14 @@ setup_multipath (struct vectors * vecs, 
 
 	set_paths_owner(vecs, mpp);
 	select_pgfailback(mpp);
+	mpp->nr_active = pathcount(mpp, PATH_UP);
+	select_no_path_retry(mpp);
+	if (mpp->no_path_retry != NO_PATH_RETRY_UNDEF) {
+		if (mpp->no_path_retry == NO_PATH_RETRY_FAIL)
+			dm_queue_if_no_path(mpp->alias, 0);
+		else
+			dm_queue_if_no_path(mpp->alias, 1);
+	}
 
 	return 0;
 out:
@@ -347,6 +370,38 @@ static sigset_t unblock_sighup(void)
 }
 
 /*
+ * mpp->no_path_retry:
+ *   -2 : queue_if_no_path enabled, never turned off
+ *   -1 : fail_if_no_path
+ *    0 : nothing
+ *   >0 : queue_if_no_path enabled, turned off after polling n times
+ */
+static void
+update_queue_mode_del_path(struct multipath *mpp)
+{
+	if (--mpp->nr_active == 0 && mpp->no_path_retry > 0) {
+		/* Enter retry mode */
+		mpp->retry_tick = mpp->no_path_retry * conf->checkint;
+		condlog(1, "%s: Entering recovery mode: max_retries=%d",
+			mpp->alias, mpp->no_path_retry);
+	}
+	condlog(2, "%s: remaining active paths: %d", mpp->alias, mpp->nr_active);
+}
+
+static void
+update_queue_mode_add_path(struct multipath *mpp)
+{
+	if (mpp->nr_active++ == 0 && mpp->no_path_retry > 0) {
+		/* come back to normal mode from retry mode */
+		mpp->retry_tick = 0;
+		dm_queue_if_no_path(mpp->alias, 1);
+		condlog(2, "%s: queue_if_no_path enabled", mpp->alias);
+		condlog(1, "%s: Recovered to normal mode", mpp->alias);
+	}
+	condlog(2, "%s: remaining active paths: %d", mpp->alias, mpp->nr_active);
+}
+
+/*
  * returns the reschedule delay
  * negative means *stop*
  */
@@ -690,6 +745,10 @@ uev_remove_path (char * devname, struct 
 		condlog(3, "%s: not in pathvec");
 		return 1;
 	}
+
+	if (pp->mpp && pp->state == PATH_UP)
+		update_queue_mode_del_path(pp->mpp);
+
 	condlog(2, "remove %s path checker", devname);
 	i = find_slot(vecs->pathvec, (void *)pp);
 	vector_del_slot(vecs->pathvec, i);
@@ -817,6 +876,13 @@ reconfigure (struct vectors * vecs)
 	vector_foreach_slot (vecs->mpvec, mpp, i) {
 		mpp->mpe = find_mpe(mpp->wwid);
 		set_paths_owner(vecs, mpp);
+		select_no_path_retry(mpp);
+		if (mpp->no_path_retry != NO_PATH_RETRY_UNDEF) {
+			if (mpp->no_path_retry == NO_PATH_RETRY_FAIL)
+				dm_queue_if_no_path(mpp->alias, 0);
+			else
+				dm_queue_if_no_path(mpp->alias, 1);
+		}
 	}
 	vector_foreach_slot (vecs->pathvec, pp, i) {
 		select_checkfn(pp);
@@ -983,6 +1049,7 @@ fail_path (struct path * pp)
 		 pp->dev_t, pp->mpp->alias);
 
 	dm_fail_path(pp->mpp->alias, pp->dev_t);
+	update_queue_mode_del_path(pp->mpp);
 }
 
 /*
@@ -991,11 +1058,14 @@ fail_path (struct path * pp)
 static void
 reinstate_path (struct path * pp)
 {
-	if (pp->mpp) {
-		if (dm_reinstate(pp->mpp->alias, pp->dev_t))
-			condlog(0, "%s: reinstate failed", pp->dev_t);
-		else
-			condlog(2, "%s: reinstated", pp->dev_t);
+	if (!pp->mpp)
+		return;
+
+	if (dm_reinstate(pp->mpp->alias, pp->dev_t))
+		condlog(0, "%s: reinstate failed", pp->dev_t);
+	else {
+		condlog(2, "%s: reinstated", pp->dev_t);
+		update_queue_mode_add_path(pp->mpp);
 	}
 }
 
@@ -1056,6 +1126,23 @@ defered_failback_tick (vector mpvec)
 	}
 }
 
+static void
+retry_count_tick(vector mpvec)
+{
+	struct multipath *mpp;
+	int i;
+
+	vector_foreach_slot (mpvec, mpp, i) {
+		if (mpp->retry_tick) {
+			condlog(4, "%s: Retrying.. No active path", mpp->alias);
+			if(--mpp->retry_tick == 0) {
+				dm_queue_if_no_path(mpp->alias, 0);
+				condlog(2, "%s: Disable queueing", mpp->alias);
+			}
+		}
+	}
+}
+
 static void *
 checkerloop (void *ap)
 {
@@ -1201,6 +1288,7 @@ checkerloop (void *ap)
 			}
 		}
 		defered_failback_tick(vecs->mpvec);
+		retry_count_tick(vecs->mpvec);
 
 		if (count)
 			count--;

Regards,
Kiyoshi Ueda


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