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dm cache: switch the "default" cache replacement policy from mq to smq

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The Stochastic multiqueue (SMQ) policy (vs MQ) offers the promise of
less memory utilization, improved performance and increased adaptability
in the face of changing workloads.  SMQ also does not have any
cumbersome tuning knobs.

Users may switch from "mq" to "smq" simply by appropriately reloading a
DM table that is using the cache target.  Doing so will cause all of the
mq policy's hints to be dropped.  Also, performance of the cache may
degrade slightly until smq recalculates the origin device's hotspots
that should be cached.

In the future the "mq" policy will just silently make use of "smq" and
the mq code will be removed.

Signed-off-by: Mike Snitzer <[email protected]>
Acked-by: Joe Thornber <[email protected]>
This commit is contained in:
Mike Snitzer 2015-06-17 11:43:38 -04:00
commit bccab6a01a
3 changed files with 86 additions and 32 deletions
Download patch file Download diff file Expand all files Collapse all files

34
drivers/md/dm-cache-policy-mq.c
View file

@ -1431,21 +1431,12 @@ bad_pre_cache_init:
static struct dm_cache_policy_type mq_policy_type = {
.name = "mq",
.version = {1, 3, 0},
.version = {1, 4, 0},
.hint_size = 4,
.owner = THIS_MODULE,
.create = mq_create
};
static struct dm_cache_policy_type default_policy_type = {
.name = "default",
.version = {1, 3, 0},
.hint_size = 4,
.owner = THIS_MODULE,
.create = mq_create,
.real = &mq_policy_type
};
static int __init mq_init(void)
{
int r;
@ -1455,36 +1446,21 @@ static int __init mq_init(void)
__alignof__(struct entry),
0, NULL);
if (!mq_entry_cache)
goto bad;
return -ENOMEM;
r = dm_cache_policy_register(&mq_policy_type);
if (r) {
DMERR("register failed %d", r);
goto bad_register_mq;
kmem_cache_destroy(mq_entry_cache);
return -ENOMEM;
}
r = dm_cache_policy_register(&default_policy_type);
if (!r) {
DMINFO("version %u.%u.%u loaded",
mq_policy_type.version[0],
mq_policy_type.version[1],
mq_policy_type.version[2]);
return 0;
}
DMERR("register failed (as default) %d", r);
dm_cache_policy_unregister(&mq_policy_type);
bad_register_mq:
kmem_cache_destroy(mq_entry_cache);
bad:
return -ENOMEM;
return 0;
}
static void __exit mq_exit(void)
{
dm_cache_policy_unregister(&mq_policy_type);
dm_cache_policy_unregister(&default_policy_type);
kmem_cache_destroy(mq_entry_cache);
}

17
drivers/md/dm-cache-policy-smq.c
View file

@ -1748,6 +1748,15 @@ static struct dm_cache_policy_type smq_policy_type = {
.create = smq_create
};
static struct dm_cache_policy_type default_policy_type = {
.name = "default",
.version = {1, 0, 0},
.hint_size = 4,
.owner = THIS_MODULE,
.create = smq_create,
.real = &smq_policy_type
};
static int __init smq_init(void)
{
int r;
@ -1758,12 +1767,20 @@ static int __init smq_init(void)
return -ENOMEM;
}
r = dm_cache_policy_register(&default_policy_type);
if (r) {
DMERR("register failed (as default) %d", r);
dm_cache_policy_unregister(&smq_policy_type);
return -ENOMEM;
}
return 0;
}
static void __exit smq_exit(void)
{
dm_cache_policy_unregister(&smq_policy_type);
dm_cache_policy_unregister(&default_policy_type);
}
module_init(smq_init);