dm: add reserved_rq_based_ios module parameter

Allow user to change the number of IOs that are reserved by
request-based DM's mempools by writing to this file:
/sys/module/dm_mod/parameters/reserved_rq_based_ios

The default value is RESERVED_REQUEST_BASED_IOS (256).  The maximum
allowed value is RESERVED_MAX_IOS (1024).

Export dm_get_reserved_rq_based_ios() for use by DM targets and core
code.  Switch to sizing dm-mpath's mempool using DM core's configurable
'reserved_rq_based_ios'.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Frank Mayhar <fmayhar@google.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>

3 files changed, 42 insertions, 4 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index e08be94959fd..de570a558764 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -7,6 +7,7 @@
 
 #include <linux/device-mapper.h>
 
+#include "dm.h"
 #include "dm-path-selector.h"
 #include "dm-uevent.h"
 
@@ -116,8 +117,6 @@ struct dm_mpath_io {
 
 typedef int (*action_fn) (struct pgpath *pgpath);
 
-#define MIN_IOS 256     /* Mempool size */
-
 static struct kmem_cache *_mpio_cache;
 
 static struct workqueue_struct *kmultipathd, *kmpath_handlerd;
@@ -190,6 +189,7 @@ static void free_priority_group(struct priority_group *pg,
 static struct multipath *alloc_multipath(struct dm_target *ti)
 {
         struct multipath *m;
+        unsigned min_ios = dm_get_reserved_rq_based_ios();
 
         m = kzalloc(sizeof(*m), GFP_KERNEL);
         if (m) {
@@ -202,7 +202,7 @@ static struct multipath *alloc_multipath(struct dm_target *ti)
                 INIT_WORK(&m->trigger_event, trigger_event);
                 init_waitqueue_head(&m->pg_init_wait);
                 mutex_init(&m->work_mutex);
-                m->mpio_pool = mempool_create_slab_pool(MIN_IOS, _mpio_cache);
+                m->mpio_pool = mempool_create_slab_pool(min_ios, _mpio_cache);
                 if (!m->mpio_pool) {
                         kfree(m);
                         return NULL;
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index f2e5a50ee84e..1e85f1da1ef3 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -213,9 +213,41 @@ struct dm_md_mempools {
 
 #define RESERVED_BIO_BASED_IOS          16
 #define RESERVED_REQUEST_BASED_IOS      256
+#define RESERVED_MAX_IOS                1024
 static struct kmem_cache *_io_cache;
 static struct kmem_cache *_rq_tio_cache;
 
+/*
+ * Request-based DM's mempools' reserved IOs set by the user.
+ */
+static unsigned reserved_rq_based_ios = RESERVED_REQUEST_BASED_IOS;
+
+static unsigned __dm_get_reserved_ios(unsigned *reserved_ios,
+                                      unsigned def, unsigned max)
+{
+        unsigned ios = ACCESS_ONCE(*reserved_ios);
+        unsigned modified_ios = 0;
+
+        if (!ios)
+                modified_ios = def;
+        else if (ios > max)
+                modified_ios = max;
+
+        if (modified_ios) {
+                (void)cmpxchg(reserved_ios, ios, modified_ios);
+                ios = modified_ios;
+        }
+
+        return ios;
+}
+
+unsigned dm_get_reserved_rq_based_ios(void)
+{
+        return __dm_get_reserved_ios(&reserved_rq_based_ios,
+                                     RESERVED_REQUEST_BASED_IOS, RESERVED_MAX_IOS);
+}
+EXPORT_SYMBOL_GPL(dm_get_reserved_rq_based_ios);
+
 static int __init local_init(void)
 {
         int r = -ENOMEM;
@@ -2878,7 +2910,7 @@ struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity, u
                 front_pad = roundup(per_bio_data_size, __alignof__(struct dm_target_io)) + offsetof(struct dm_target_io, clone);
         } else if (type == DM_TYPE_REQUEST_BASED) {
                 cachep = _rq_tio_cache;
-                pool_size = RESERVED_REQUEST_BASED_IOS;
+                pool_size = dm_get_reserved_rq_based_ios();
                 front_pad = offsetof(struct dm_rq_clone_bio_info, clone);
                 /* per_bio_data_size is not used. See __bind_mempools(). */
                 WARN_ON(per_bio_data_size != 0);
@@ -2936,6 +2968,10 @@ module_exit(dm_exit);
 
 module_param(major, uint, 0);
 MODULE_PARM_DESC(major, "The major number of the device mapper");
+
+module_param(reserved_rq_based_ios, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(reserved_rq_based_ios, "Reserved IOs in request-based mempools");
+
 MODULE_DESCRIPTION(DM_NAME " driver");
 MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
 MODULE_LICENSE("GPL");
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 5e604cc7b4aa..15396501e0b3 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -184,6 +184,8 @@ void dm_free_md_mempools(struct dm_md_mempools *pools);
 /*
  * Helpers that are used by DM core
  */
+unsigned dm_get_reserved_rq_based_ios(void);
+
 static inline bool dm_message_test_buffer_overflow(char *result, unsigned maxlen)
 {
         return !maxlen || strlen(result) + 1 >= maxlen;