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Commit ed8b752b authored by Mike Snitzer's avatar Mike Snitzer Committed by Alasdair G Kergon
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dm table: set flush capability based on underlying devices 



DM has always advertised both REQ_FLUSH and REQ_FUA flush capabilities
regardless of whether or not a given DM device's underlying devices
also advertised a need for them.

Block's flush-merge changes from 2.6.39 have proven to be more costly
for DM devices.  Performance regressions have been reported even when
DM's underlying devices do not advertise that they have a write cache.

Fix the performance regressions by configuring a DM device's flushing
capabilities based on those of the underlying devices' capabilities.

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 772ae5f5

drivers/md/dm-table.c

+43 −0
Original line number Diff line number Diff line
@@ -1248,9 +1248,45 @@ static void dm_table_set_integrity(struct dm_table *t) 
			       blk_get_integrity(template_disk));

}



static int device_flush_capable(struct dm_target *ti, struct dm_dev *dev,

				sector_t start, sector_t len, void *data)

{

	unsigned flush = (*(unsigned *)data);

	struct request_queue *q = bdev_get_queue(dev->bdev);



	return q && (q->flush_flags & flush);

}



static bool dm_table_supports_flush(struct dm_table *t, unsigned flush)

{

	struct dm_target *ti;

	unsigned i = 0;



	/*

	 * Require at least one underlying device to support flushes.

	 * t->devices includes internal dm devices such as mirror logs

	 * so we need to use iterate_devices here, which targets

	 * supporting flushes must provide.

	 */

	while (i < dm_table_get_num_targets(t)) {

		ti = dm_table_get_target(t, i++);



		if (!ti->num_flush_requests)

			continue;



		if (ti->type->iterate_devices &&

		    ti->type->iterate_devices(ti, device_flush_capable, &flush))

			return 1;

	}



	return 0;

}



void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,

			       struct queue_limits *limits)

{

	unsigned flush = 0;



	/*

	 * Copy table's limits to the DM device's request_queue

	 */
@@ -1261,6 +1297,13 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q, 
	else

		queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);



	if (dm_table_supports_flush(t, REQ_FLUSH)) {

		flush |= REQ_FLUSH;

		if (dm_table_supports_flush(t, REQ_FUA))

			flush |= REQ_FUA;

	}

	blk_queue_flush(q, flush);



	dm_table_set_integrity(t);



	/*

drivers/md/dm.c

+0 −1
Original line number Diff line number Diff line
@@ -1808,7 +1808,6 @@ static void dm_init_md_queue(struct mapped_device *md) 
	blk_queue_make_request(md->queue, dm_request);

	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);

	blk_queue_merge_bvec(md->queue, dm_merge_bvec);

	blk_queue_flush(md->queue, REQ_FLUSH | REQ_FUA);

}



/*