dm io: use fixed initial mempool size

Replace the arbitrary calculation of an initial io struct mempool size
with a constant.

The code calculated the number of reserved structures based on the request
size and used a "magic" multiplication constant of 4.  This patch changes
it to reserve a fixed number - itself still chosen quite arbitrarily.
Further testing might show if there is a better number to choose.

Note that if there is no memory pressure, we can still allocate an
arbitrary number of "struct io" structures.  One structure is enough to
process the whole request.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

6 files changed, 10 insertions, 41 deletions

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 76a5af00a26b..2067288f61f9 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -19,6 +19,8 @@
 #define DM_MSG_PREFIX "io"
 
 #define DM_IO_MAX_REGIONS       BITS_PER_LONG
+#define MIN_IOS         16
+#define MIN_BIOS        16
 
 struct dm_io_client {
         mempool_t *pool;
@@ -41,33 +43,21 @@ struct io {
 static struct kmem_cache *_dm_io_cache;
 
 /*
- * io contexts are only dynamically allocated for asynchronous
- * io.  Since async io is likely to be the majority of io we'll
- * have the same number of io contexts as bios! (FIXME: must reduce this).
- */
-
-static unsigned int pages_to_ios(unsigned int pages)
-{
-        return 4 * pages;       /* too many ? */
-}
-
-/*
  * Create a client with mempool and bioset.
  */
-struct dm_io_client *dm_io_client_create(unsigned num_pages)
+struct dm_io_client *dm_io_client_create(void)
 {
-        unsigned ios = pages_to_ios(num_pages);
         struct dm_io_client *client;
 
         client = kmalloc(sizeof(*client), GFP_KERNEL);
         if (!client)
                 return ERR_PTR(-ENOMEM);
 
-        client->pool = mempool_create_slab_pool(ios, _dm_io_cache);
+        client->pool = mempool_create_slab_pool(MIN_IOS, _dm_io_cache);
         if (!client->pool)
                 goto bad;
 
-        client->bios = bioset_create(16, 0);
+        client->bios = bioset_create(MIN_BIOS, 0);
         if (!client->bios)
                 goto bad;
 
@@ -81,13 +71,6 @@ struct dm_io_client *dm_io_client_create(unsigned num_pages)
 }
 EXPORT_SYMBOL(dm_io_client_create);
 
-int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client)
-{
-        return mempool_resize(client->pool, pages_to_ios(num_pages),
-                              GFP_KERNEL);
-}
-EXPORT_SYMBOL(dm_io_client_resize);
-
 void dm_io_client_destroy(struct dm_io_client *client)
 {
         mempool_destroy(client->pool);
diff --git a/drivers/md/dm-kcopyd.c b/drivers/md/dm-kcopyd.c
index 5dfbdcb40a47..719693340d1d 100644
--- a/drivers/md/dm-kcopyd.c
+++ b/drivers/md/dm-kcopyd.c
@@ -667,7 +667,7 @@ int dm_kcopyd_client_create(unsigned min_pages,
         if (r)
                 goto bad_client_pages;
 
-        kc->io_client = dm_io_client_create(min_pages);
+        kc->io_client = dm_io_client_create();
         if (IS_ERR(kc->io_client)) {
                 r = PTR_ERR(kc->io_client);
                 goto bad_io_client;
diff --git a/drivers/md/dm-log.c b/drivers/md/dm-log.c
index a1f321889676..948e3f4925bf 100644
--- a/drivers/md/dm-log.c
+++ b/drivers/md/dm-log.c
@@ -449,8 +449,7 @@ static int create_log_context(struct dm_dirty_log *log, struct dm_target *ti,
 
                 lc->io_req.mem.type = DM_IO_VMA;
                 lc->io_req.notify.fn = NULL;
-                lc->io_req.client = dm_io_client_create(dm_div_up(buf_size,
-                                                                   PAGE_SIZE));
+                lc->io_req.client = dm_io_client_create();
                 if (IS_ERR(lc->io_req.client)) {
                         r = PTR_ERR(lc->io_req.client);
                         DMWARN("couldn't allocate disk io client");
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 976ad4688afc..53089aa11387 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -22,7 +22,6 @@
 #define DM_MSG_PREFIX "raid1"
 
 #define MAX_RECOVERY 1  /* Maximum number of regions recovered in parallel. */
-#define DM_IO_PAGES 64
 #define DM_KCOPYD_PAGES 64
 
 #define DM_RAID1_HANDLE_ERRORS 0x01
@@ -887,7 +886,7 @@ static struct mirror_set *alloc_context(unsigned int nr_mirrors,
                 return NULL;
         }
 
-        ms->io_client = dm_io_client_create(DM_IO_PAGES);
+        ms->io_client = dm_io_client_create();
         if (IS_ERR(ms->io_client)) {
                 ti->error = "Error creating dm_io client";
                 mempool_destroy(ms->read_record_pool);
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index 95891dfcbca0..135c2f1fdbfc 100644
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -154,11 +154,6 @@ struct pstore {
         struct workqueue_struct *metadata_wq;
 };
 
-static unsigned sectors_to_pages(unsigned sectors)
-{
-        return DIV_ROUND_UP(sectors, PAGE_SIZE >> 9);
-}
-
 static int alloc_area(struct pstore *ps)
 {
         int r = -ENOMEM;
@@ -318,8 +313,7 @@ static int read_header(struct pstore *ps, int *new_snapshot)
                 chunk_size_supplied = 0;
         }
 
-        ps->io_client = dm_io_client_create(sectors_to_pages(ps->store->
-                                                             chunk_size));
+        ps->io_client = dm_io_client_create();
         if (IS_ERR(ps->io_client))
                 return PTR_ERR(ps->io_client);
 
@@ -368,11 +362,6 @@ static int read_header(struct pstore *ps, int *new_snapshot)
                 return r;
         }
 
-        r = dm_io_client_resize(sectors_to_pages(ps->store->chunk_size),
-                                ps->io_client);
-        if (r)
-                return r;
-
         r = alloc_area(ps);
         return r;
 
diff --git a/include/linux/dm-io.h b/include/linux/dm-io.h
index 5c9186b93fff..f4b0aa3126f5 100644
--- a/include/linux/dm-io.h
+++ b/include/linux/dm-io.h
@@ -69,8 +69,7 @@ struct dm_io_request {
  *
  * Create/destroy may block.
  */
-struct dm_io_client *dm_io_client_create(unsigned num_pages);
-int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client);
+struct dm_io_client *dm_io_client_create(void);
 void dm_io_client_destroy(struct dm_io_client *client);
 
 /*