Commit 5c0de3d7 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
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dm writecache: make writeback pause configurable 



Commit 95b88f4d ("dm writecache: pause
writeback if cache full and origin being written directly") introduced a
code that pauses cache flushing if we are issuing writes directly to the
origin.

Improve that initial commit by making the timeout code configurable
(via the option "pause_writeback"). Also change the default from 1s to
3s because it performed better.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 95b88f4d

Documentation/admin-guide/device-mapper/writecache.rst

+3 −2
Original line number Diff line number Diff line
@@ -12,7 +12,6 @@ first sector should contain valid superblock from previous invocation. 
Constructor parameters:



1. type of the cache device - "p" or "s"



	- p - persistent memory

	- s - SSD

2. the underlying device that will be cached
@@ -21,7 +20,6 @@ Constructor parameters: 
   size)

5. the number of optional parameters (the parameters with an argument

   count as two)



	start_sector n		(default: 0)

		offset from the start of cache device in 512-byte sectors

	high_watermark n	(default: 50)
@@ -71,6 +69,9 @@ Constructor parameters: 
	metadata_only

		only metadata is promoted to the cache. This option

		improves performance for heavier REQ_META workloads.

	pause_writeback n	(default: 3000)

		pause writeback if there was some write I/O redirected to

		the origin volume in the last n milliseconds



Status:

1. error indicator - 0 if there was no error, otherwise error number

drivers/md/dm-io-tracker.h

+12 −0
Original line number Diff line number Diff line
@@ -45,6 +45,18 @@ static inline bool dm_iot_idle_for(struct dm_io_tracker *iot, unsigned long j) 
	return r;

}



static inline unsigned long dm_iot_idle_time(struct dm_io_tracker *iot)

{

	unsigned long r = 0;



	spin_lock_irq(&iot->lock);

	if (!iot->in_flight)

		r = jiffies - iot->idle_time;

	spin_unlock_irq(&iot->lock);



	return r;

}



static inline void dm_iot_io_begin(struct dm_io_tracker *iot, sector_t len)

{

	spin_lock_irq(&iot->lock);

drivers/md/dm-writecache.c

+40 −8
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 
#define AUTOCOMMIT_MSEC			1000

#define MAX_AGE_DIV			16

#define MAX_AGE_UNSPECIFIED		-1UL

#define PAUSE_WRITEBACK			(HZ * 3)



#define BITMAP_GRANULARITY	65536

#if BITMAP_GRANULARITY < PAGE_SIZE
@@ -125,6 +126,7 @@ struct dm_writecache { 
	size_t freelist_high_watermark;

	size_t freelist_low_watermark;

	unsigned long max_age;

	unsigned long pause;



	unsigned uncommitted_blocks;

	unsigned autocommit_blocks;
@@ -174,11 +176,13 @@ struct dm_writecache { 
	bool cleaner:1;

	bool cleaner_set:1;

	bool metadata_only:1;

	bool pause_set:1;



	unsigned high_wm_percent_value;

	unsigned low_wm_percent_value;

	unsigned autocommit_time_value;

	unsigned max_age_value;

	unsigned pause_value;



	unsigned writeback_all;

	struct workqueue_struct *writeback_wq;
@@ -1470,10 +1474,12 @@ static int writecache_map(struct dm_target *ti, struct bio *bio) 
	}



unlock_remap_origin:

	if (bio_data_dir(bio) != READ) {

	if (likely(wc->pause != 0)) {

		 if (bio_op(bio) == REQ_OP_WRITE) {

			dm_iot_io_begin(&wc->iot, 1);

			bio->bi_private = (void *)2;

		}

	}

	bio_set_dev(bio, wc->dev->bdev);

	wc_unlock(wc);

	return DM_MAPIO_REMAPPED;
@@ -1837,10 +1843,19 @@ static void writecache_writeback(struct work_struct *work) 
		dm_kcopyd_client_flush(wc->dm_kcopyd);

	}



	if (!wc->writeback_all && !dm_suspended(wc->ti)) {

		while (!dm_iot_idle_for(&wc->iot, HZ)) {

			cond_resched();

			msleep(1000);

	if (likely(wc->pause != 0)) {

		while (1) {

			unsigned long idle;

			if (unlikely(wc->cleaner) || unlikely(wc->writeback_all) ||

			    unlikely(dm_suspended(wc->ti)))

				break;

			idle = dm_iot_idle_time(&wc->iot);

			if (idle >= wc->pause)

				break;

			idle = wc->pause - idle;

			if (idle > HZ)

				idle = HZ;

			schedule_timeout_idle(idle);

		}

	}
@@ -2113,7 +2128,7 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv) 
	struct wc_memory_superblock s;



	static struct dm_arg _args[] = {

		{0, 17, "Invalid number of feature args"},

		{0, 18, "Invalid number of feature args"},

	};



	as.argc = argc;
@@ -2206,6 +2221,7 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv) 
			goto bad;

		}

	} else {

		wc->pause = PAUSE_WRITEBACK;

		r = mempool_init_kmalloc_pool(&wc->copy_pool, 1, sizeof(struct copy_struct));

		if (r) {

			ti->error = "Could not allocate mempool";
@@ -2344,6 +2360,18 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv) 
			} else goto invalid_optional;

		} else if (!strcasecmp(string, "metadata_only")) {

			wc->metadata_only = true;

		} else if (!strcasecmp(string, "pause_writeback") && opt_params >= 1) {

			unsigned pause_msecs;

			if (WC_MODE_PMEM(wc))

				goto invalid_optional;

			string = dm_shift_arg(&as), opt_params--;

			if (sscanf(string, "%u%c", &pause_msecs, &dummy) != 1)

				goto invalid_optional;

			if (pause_msecs > 60000)

				goto invalid_optional;

			wc->pause = msecs_to_jiffies(pause_msecs);

			wc->pause_set = true;

			wc->pause_value = pause_msecs;

		} else {

invalid_optional:

			r = -EINVAL;
@@ -2569,6 +2597,8 @@ static void writecache_status(struct dm_target *ti, status_type_t type, 
			extra_args++;

		if (wc->metadata_only)

			extra_args++;

		if (wc->pause_set)

			extra_args += 2;



		DMEMIT("%u", extra_args);

		if (wc->start_sector_set)
@@ -2591,6 +2621,8 @@ static void writecache_status(struct dm_target *ti, status_type_t type, 
			DMEMIT(" %sfua", wc->writeback_fua ? "" : "no");

		if (wc->metadata_only)

			DMEMIT(" metadata_only");

		if (wc->pause_set)

			DMEMIT(" pause_writeback %u", wc->pause_value);

		break;

	}

}