Commit 67324ea1 authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm thin: sort the per thin deferred bios using an rb_tree 



A thin-pool will allocate blocks using FIFO order for all thin devices
which share the thin-pool.  Because of this simplistic allocation the
thin-pool's space can become fragmented quite easily; especially when
multiple threads are requesting blocks in parallel.

Sort each thin device's deferred_bio_list based on logical sector to
help reduce fragmentation of the thin-pool's ondisk layout.

The following tables illustrate the realized gains/potential offered by
sorting each thin device's deferred_bio_list.  An "io size"-sized random
read of the device would result in "seeks/io" fragments being read, with
an average "distance/seek" between each fragment.

Data was written to a single thin device using multiple threads via
iozone (8 threads, 64K for both the block_size and io_size).

unsorted:

     io size   seeks/io distance/seek
  --------------------------------------
          4k    0.000   0b
         16k    0.013   11m
         64k    0.065   11m
        256k    0.274   10m
          1m    1.109   10m
          4m    4.411   10m
         16m    17.097  11m
         64m    60.055  13m
        256m    148.798 25m
          1g    809.929 21m

sorted:

     io size   seeks/io distance/seek
  --------------------------------------
          4k    0.000   0b
         16k    0.000   1g
         64k    0.001   1g
        256k    0.003   1g
          1m    0.011   1g
          4m    0.045   1g
         16m    0.181   1g
         64m    0.747   1011m
        256m    3.299   1g
          1g    14.373  1g

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Acked-by: default avatarJoe Thornber <ejt@redhat.com>
parent c140e1c4

drivers/md/dm-thin.c

+82 −2
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/init.h>

#include <linux/module.h>

#include <linux/slab.h>

#include <linux/rbtree.h>



#define	DM_MSG_PREFIX	"thin"
@@ -230,6 +231,7 @@ struct thin_c { 
	spinlock_t lock;

	struct bio_list deferred_bio_list;

	struct bio_list retry_on_resume_list;

	struct rb_root sort_bio_list; /* sorted list of deferred bios */

};



/*----------------------------------------------------------------*/
@@ -371,6 +373,7 @@ struct dm_thin_endio_hook { 
	struct dm_deferred_entry *shared_read_entry;

	struct dm_deferred_entry *all_io_entry;

	struct dm_thin_new_mapping *overwrite_mapping;

	struct rb_node rb_node;

};



static void requeue_bio_list(struct thin_c *tc, struct bio_list *master)
@@ -1367,12 +1370,77 @@ static int need_commit_due_to_time(struct pool *pool) 
	       jiffies > pool->last_commit_jiffies + COMMIT_PERIOD;

}



#define thin_pbd(node) rb_entry((node), struct dm_thin_endio_hook, rb_node)

#define thin_bio(pbd) dm_bio_from_per_bio_data((pbd), sizeof(struct dm_thin_endio_hook))



static void __thin_bio_rb_add(struct thin_c *tc, struct bio *bio)

{

	struct rb_node **rbp, *parent;

	struct dm_thin_endio_hook *pbd;

	sector_t bi_sector = bio->bi_iter.bi_sector;



	rbp = &tc->sort_bio_list.rb_node;

	parent = NULL;

	while (*rbp) {

		parent = *rbp;

		pbd = thin_pbd(parent);



		if (bi_sector < thin_bio(pbd)->bi_iter.bi_sector)

			rbp = &(*rbp)->rb_left;

		else

			rbp = &(*rbp)->rb_right;

	}



	pbd = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));

	rb_link_node(&pbd->rb_node, parent, rbp);

	rb_insert_color(&pbd->rb_node, &tc->sort_bio_list);

}



static void __extract_sorted_bios(struct thin_c *tc)

{

	struct rb_node *node;

	struct dm_thin_endio_hook *pbd;

	struct bio *bio;



	for (node = rb_first(&tc->sort_bio_list); node; node = rb_next(node)) {

		pbd = thin_pbd(node);

		bio = thin_bio(pbd);



		bio_list_add(&tc->deferred_bio_list, bio);

		rb_erase(&pbd->rb_node, &tc->sort_bio_list);

	}



	WARN_ON(!RB_EMPTY_ROOT(&tc->sort_bio_list));

}



static void __sort_thin_deferred_bios(struct thin_c *tc)

{

	struct bio *bio;

	struct bio_list bios;



	bio_list_init(&bios);

	bio_list_merge(&bios, &tc->deferred_bio_list);

	bio_list_init(&tc->deferred_bio_list);



	/* Sort deferred_bio_list using rb-tree */

	while ((bio = bio_list_pop(&bios)))

		__thin_bio_rb_add(tc, bio);



	/*

	 * Transfer the sorted bios in sort_bio_list back to

	 * deferred_bio_list to allow lockless submission of

	 * all bios.

	 */

	__extract_sorted_bios(tc);

}



static void process_thin_deferred_bios(struct thin_c *tc)

{

	struct pool *pool = tc->pool;

	unsigned long flags;

	struct bio *bio;

	struct bio_list bios;

	struct blk_plug plug;



	if (tc->requeue_mode) {

		requeue_bio_list(tc, &tc->deferred_bio_list);
@@ -1382,10 +1450,20 @@ static void process_thin_deferred_bios(struct thin_c *tc) 
	bio_list_init(&bios);



	spin_lock_irqsave(&tc->lock, flags);



	if (bio_list_empty(&tc->deferred_bio_list)) {

		spin_unlock_irqrestore(&tc->lock, flags);

		return;

	}



	__sort_thin_deferred_bios(tc);



	bio_list_merge(&bios, &tc->deferred_bio_list);

	bio_list_init(&tc->deferred_bio_list);



	spin_unlock_irqrestore(&tc->lock, flags);



	blk_start_plug(&plug);

	while ((bio = bio_list_pop(&bios))) {

		/*

		 * If we've got no free new_mapping structs, and processing
@@ -1405,6 +1483,7 @@ static void process_thin_deferred_bios(struct thin_c *tc) 
		else

			pool->process_bio(tc, bio);

	}

	blk_finish_plug(&plug);

}



static void process_deferred_bios(struct pool *pool)
@@ -2964,7 +3043,7 @@ static struct target_type pool_target = { 
	.name = "thin-pool",

	.features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |

		    DM_TARGET_IMMUTABLE,

	.version = {1, 11, 0},

	.version = {1, 12, 0},

	.module = THIS_MODULE,

	.ctr = pool_ctr,

	.dtr = pool_dtr,
@@ -3040,6 +3119,7 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv) 
	spin_lock_init(&tc->lock);

	bio_list_init(&tc->deferred_bio_list);

	bio_list_init(&tc->retry_on_resume_list);

	tc->sort_bio_list = RB_ROOT;



	if (argc == 3) {

		r = dm_get_device(ti, argv[2], FMODE_READ, &origin_dev);
@@ -3287,7 +3367,7 @@ static int thin_iterate_devices(struct dm_target *ti, 


static struct target_type thin_target = {

	.name = "thin",

	.version = {1, 11, 0},

	.version = {1, 12, 0},

	.module	= THIS_MODULE,

	.ctr = thin_ctr,

	.dtr = thin_dtr,

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