Commit df5d2e90 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon

dm kcopyd: introduce configurable throttling

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent a2606241
......@@ -22,6 +22,7 @@
#include <linux/vmalloc.h>
#include <linux/workqueue.h>
#include <linux/mutex.h>
#include <linux/delay.h>
#include <linux/device-mapper.h>
#include <linux/dm-kcopyd.h>
......@@ -51,6 +52,8 @@ struct dm_kcopyd_client {
struct workqueue_struct *kcopyd_wq;
struct work_struct kcopyd_work;
struct dm_kcopyd_throttle *throttle;
/*
* We maintain three lists of jobs:
*
......@@ -68,6 +71,117 @@ struct dm_kcopyd_client {
static struct page_list zero_page_list;
static DEFINE_SPINLOCK(throttle_spinlock);
/*
* IO/IDLE accounting slowly decays after (1 << ACCOUNT_INTERVAL_SHIFT) period.
* When total_period >= (1 << ACCOUNT_INTERVAL_SHIFT) the counters are divided
* by 2.
*/
#define ACCOUNT_INTERVAL_SHIFT SHIFT_HZ
/*
* Sleep this number of milliseconds.
*
* The value was decided experimentally.
* Smaller values seem to cause an increased copy rate above the limit.
* The reason for this is unknown but possibly due to jiffies rounding errors
* or read/write cache inside the disk.
*/
#define SLEEP_MSEC 100
/*
* Maximum number of sleep events. There is a theoretical livelock if more
* kcopyd clients do work simultaneously which this limit avoids.
*/
#define MAX_SLEEPS 10
static void io_job_start(struct dm_kcopyd_throttle *t)
{
unsigned throttle, now, difference;
int slept = 0, skew;
if (unlikely(!t))
return;
try_again:
spin_lock_irq(&throttle_spinlock);
throttle = ACCESS_ONCE(t->throttle);
if (likely(throttle >= 100))
goto skip_limit;
now = jiffies;
difference = now - t->last_jiffies;
t->last_jiffies = now;
if (t->num_io_jobs)
t->io_period += difference;
t->total_period += difference;
/*
* Maintain sane values if we got a temporary overflow.
*/
if (unlikely(t->io_period > t->total_period))
t->io_period = t->total_period;
if (unlikely(t->total_period >= (1 << ACCOUNT_INTERVAL_SHIFT))) {
int shift = fls(t->total_period >> ACCOUNT_INTERVAL_SHIFT);
t->total_period >>= shift;
t->io_period >>= shift;
}
skew = t->io_period - throttle * t->total_period / 100;
if (unlikely(skew > 0) && slept < MAX_SLEEPS) {
slept++;
spin_unlock_irq(&throttle_spinlock);
msleep(SLEEP_MSEC);
goto try_again;
}
skip_limit:
t->num_io_jobs++;
spin_unlock_irq(&throttle_spinlock);
}
static void io_job_finish(struct dm_kcopyd_throttle *t)
{
unsigned long flags;
if (unlikely(!t))
return;
spin_lock_irqsave(&throttle_spinlock, flags);
t->num_io_jobs--;
if (likely(ACCESS_ONCE(t->throttle) >= 100))
goto skip_limit;
if (!t->num_io_jobs) {
unsigned now, difference;
now = jiffies;
difference = now - t->last_jiffies;
t->last_jiffies = now;
t->io_period += difference;
t->total_period += difference;
/*
* Maintain sane values if we got a temporary overflow.
*/
if (unlikely(t->io_period > t->total_period))
t->io_period = t->total_period;
}
skip_limit:
spin_unlock_irqrestore(&throttle_spinlock, flags);
}
static void wake(struct dm_kcopyd_client *kc)
{
queue_work(kc->kcopyd_wq, &kc->kcopyd_work);
......@@ -348,6 +462,8 @@ static void complete_io(unsigned long error, void *context)
struct kcopyd_job *job = (struct kcopyd_job *) context;
struct dm_kcopyd_client *kc = job->kc;
io_job_finish(kc->throttle);
if (error) {
if (job->rw & WRITE)
job->write_err |= error;
......@@ -389,6 +505,8 @@ static int run_io_job(struct kcopyd_job *job)
.client = job->kc->io_client,
};
io_job_start(job->kc->throttle);
if (job->rw == READ)
r = dm_io(&io_req, 1, &job->source, NULL);
else
......@@ -695,7 +813,7 @@ int kcopyd_cancel(struct kcopyd_job *job, int block)
/*-----------------------------------------------------------------
* Client setup
*---------------------------------------------------------------*/
struct dm_kcopyd_client *dm_kcopyd_client_create(void)
struct dm_kcopyd_client *dm_kcopyd_client_create(struct dm_kcopyd_throttle *throttle)
{
int r = -ENOMEM;
struct dm_kcopyd_client *kc;
......@@ -708,6 +826,7 @@ struct dm_kcopyd_client *dm_kcopyd_client_create(void)
INIT_LIST_HEAD(&kc->complete_jobs);
INIT_LIST_HEAD(&kc->io_jobs);
INIT_LIST_HEAD(&kc->pages_jobs);
kc->throttle = throttle;
kc->job_pool = mempool_create_slab_pool(MIN_JOBS, _job_cache);
if (!kc->job_pool)
......
......@@ -82,6 +82,9 @@ struct mirror_set {
struct mirror mirror[0];
};
DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(raid1_resync_throttle,
"A percentage of time allocated for raid resynchronization");
static void wakeup_mirrord(void *context)
{
struct mirror_set *ms = context;
......@@ -1111,7 +1114,7 @@ static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv)
goto err_destroy_wq;
}
ms->kcopyd_client = dm_kcopyd_client_create();
ms->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
if (IS_ERR(ms->kcopyd_client)) {
r = PTR_ERR(ms->kcopyd_client);
goto err_destroy_wq;
......
......@@ -124,6 +124,9 @@ struct dm_snapshot {
#define RUNNING_MERGE 0
#define SHUTDOWN_MERGE 1
DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
"A percentage of time allocated for copy on write");
struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
{
return s->origin;
......@@ -1108,7 +1111,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
goto bad_hash_tables;
}
s->kcopyd_client = dm_kcopyd_client_create();
s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
if (IS_ERR(s->kcopyd_client)) {
r = PTR_ERR(s->kcopyd_client);
ti->error = "Could not create kcopyd client";
......
......@@ -26,6 +26,9 @@
#define PRISON_CELLS 1024
#define COMMIT_PERIOD HZ
DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
"A percentage of time allocated for copy on write");
/*
* The block size of the device holding pool data must be
* between 64KB and 1GB.
......@@ -1642,7 +1645,7 @@ static struct pool *pool_create(struct mapped_device *pool_md,
goto bad_prison;
}
pool->copier = dm_kcopyd_client_create();
pool->copier = dm_kcopyd_client_create(&dm_kcopyd_throttle);
if (IS_ERR(pool->copier)) {
r = PTR_ERR(pool->copier);
*error = "Error creating pool's kcopyd client";
......
......@@ -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);
/*
......
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