dm: allocate struct mapped_device with kvzalloc

The structure srcu_struct can be very big, its size is proportional to the
value CONFIG_NR_CPUS. The Fedora kernel has CONFIG_NR_CPUS 8192, the field
io_barrier in the struct mapped_device has 84kB in the debugging kernel
and 50kB in the non-debugging kernel. The large size may result in failure
of the function kzalloc_node.

In order to avoid the allocation failure, we use the function
kvzalloc_node, this function falls back to vmalloc if a large contiguous
chunk of memory is not available. This patch also moves the field
io_barrier to the last position of struct mapped_device - the reason is
that on many processor architectures, short memory offsets result in
smaller code than long memory offsets - on x86-64 it reduces code size by
320 bytes.

Note to stable kernel maintainers - the kernels 4.11 and older don't have
the function kvzalloc_node, you can use the function vzalloc_node instead.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index 2031447..6a14f94 100644 (file)
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -29,7 +29,6 @@ struct dm_kobject_holder {
  * DM targets must _not_ deference a mapped_device to directly access its members!
  */
 struct mapped_device {
-       struct srcu_struct io_barrier;
        struct mutex suspend_lock;
 
        /*
@@ -127,6 +126,8 @@ struct mapped_device {
        struct blk_mq_tag_set *tag_set;
        bool use_blk_mq:1;
        bool init_tio_pdu:1;
+
+       struct srcu_struct io_barrier;
 };
 
 void dm_init_md_queue(struct mapped_device *md);

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index be12f3f..adb874c 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1697,7 +1697,7 @@ static struct mapped_device *alloc_dev(int minor)
        struct mapped_device *md;
        void *old_md;
 
-       md = kzalloc_node(sizeof(*md), GFP_KERNEL, numa_node_id);
+       md = kvzalloc_node(sizeof(*md), GFP_KERNEL, numa_node_id);
        if (!md) {
                DMWARN("unable to allocate device, out of memory.");
                return NULL;
@@ -1797,7 +1797,7 @@ bad_io_barrier:
 bad_minor:
        module_put(THIS_MODULE);
 bad_module_get:
-       kfree(md);
+       kvfree(md);
        return NULL;
 }
 
@@ -1816,7 +1816,7 @@ static void free_dev(struct mapped_device *md)
        free_minor(minor);
 
        module_put(THIS_MODULE);
-       kfree(md);
+       kvfree(md);
 }
 
 static void __bind_mempools(struct mapped_device *md, struct dm_table *t)