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Subject[patch 036/100] dm raid1: switch read_record from kmalloc to slab to save memory
-stable review patch.  If anyone has any objections, please let us know.
---------------------

From: Mikulas Patocka <mpatocka@redhat.com>

upstream commit: 95f8fac8dc6139fedfb87746e0c8fda9b803cb46

With my previous patch to save bi_io_vec, the size of dm_raid1_read_record
is significantly increased (the vector list takes 3072 bytes on 32-bit machines
and 4096 bytes on 64-bit machines).

The structure dm_raid1_read_record used to be allocated with kmalloc,
but kmalloc aligns the size on the next power-of-two so an object
slightly greater than 4096 will allocate 8192 bytes of memory and half of
that memory will be wasted.

This patch turns kmalloc into a slab cache which doesn't have this
padding so it will reduce the memory consumed.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
drivers/md/dm-raid1.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)

--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -145,6 +145,8 @@ struct dm_raid1_read_record {
struct dm_bio_details details;
};

+static struct kmem_cache *_dm_raid1_read_record_cache;
+
/*
* Every mirror should look like this one.
*/
@@ -764,9 +766,9 @@ static struct mirror_set *alloc_context(
atomic_set(&ms->suspend, 0);
atomic_set(&ms->default_mirror, DEFAULT_MIRROR);

- len = sizeof(struct dm_raid1_read_record);
- ms->read_record_pool = mempool_create_kmalloc_pool(MIN_READ_RECORDS,
- len);
+ ms->read_record_pool = mempool_create_slab_pool(MIN_READ_RECORDS,
+ _dm_raid1_read_record_cache);
+
if (!ms->read_record_pool) {
ti->error = "Error creating mirror read_record_pool";
kfree(ms);
@@ -1279,16 +1281,31 @@ static int __init dm_mirror_init(void)
{
int r;

+ _dm_raid1_read_record_cache = KMEM_CACHE(dm_raid1_read_record, 0);
+ if (!_dm_raid1_read_record_cache) {
+ DMERR("Can't allocate dm_raid1_read_record cache");
+ r = -ENOMEM;
+ goto bad_cache;
+ }
+
r = dm_register_target(&mirror_target);
- if (r < 0)
+ if (r < 0) {
DMERR("Failed to register mirror target");
+ goto bad_target;
+ }
+
+ return 0;

+bad_target:
+ kmem_cache_destroy(_dm_raid1_read_record_cache);
+bad_cache:
return r;
}

static void __exit dm_mirror_exit(void)
{
dm_unregister_target(&mirror_target);
+ kmem_cache_destroy(_dm_raid1_read_record_cache);
}

/* Module hooks */


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