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dm kcopyd: introduce configurable throttling

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This patch allows the administrator to reduce the rate at which kcopyd
issues I/O.

Each module that uses kcopyd acquires a throttle parameter that can be
set in /sys/module/*/parameters.

We maintain a history of kcopyd usage by each module in the variables
io_period and total_period in struct dm_kcopyd_throttle. The actual
kcopyd activity is calculated as a percentage of time equal to
"(100 * io_period / total_period)".  This is compared with the user-defined
throttle percentage threshold and if it is exceeded, we sleep.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka 2013-03-01 22:45:49 +00:00 • committed by Alasdair G Kergon
parent a26062416e
commit df5d2e9089
5 changed files with 156 additions and 5 deletions
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25
include/linux/dm-kcopyd.h
View file

@ -21,11 +21,34 @@
#define DM_KCOPYD_IGNORE_ERROR 1
struct dm_kcopyd_throttle {
unsigned throttle;
unsigned num_io_jobs;
unsigned io_period;
unsigned total_period;
unsigned last_jiffies;
};
/*
* kcopyd clients that want to support throttling must pass an initialised
* dm_kcopyd_throttle struct into dm_kcopyd_client_create().
* Two or more clients may share the same instance of this struct between
* them if they wish to be throttled as a group.
*
* This macro also creates a corresponding module parameter to configure
* the amount of throttling.
*/
#define DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(name, description) \
static struct dm_kcopyd_throttle dm_kcopyd_throttle = { 100, 0, 0, 0, 0 }; \
module_param_named(name, dm_kcopyd_throttle.throttle, uint, 0644); \
MODULE_PARM_DESC(name, description)
/*
* To use kcopyd you must first create a dm_kcopyd_client object.
* throttle can be NULL if you don't want any throttling.
*/
struct dm_kcopyd_client;
struct dm_kcopyd_client *dm_kcopyd_client_create(void);
struct dm_kcopyd_client *dm_kcopyd_client_create(struct dm_kcopyd_throttle *throttle);
void dm_kcopyd_client_destroy(struct dm_kcopyd_client *kc);
/*