Commit 95f8fac8 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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dm raid1: switch read_record from kmalloc to slab to save memory 



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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent a920f6b3

drivers/md/dm-raid1.c

+21 −4
Original line number Diff line number Diff line
@@ -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(unsigned int nr_mirrors, 
	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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