Commit f3ac8bf7 authored by NeilBrown's avatar NeilBrown
Browse files

md: tidy up device searches in read_balance. 



The code for searching through the device list to read-balance in
raid1 is rather clumsy and hard to follow.  Try to simplify it a bit.

No important functionality change here.


Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 046abeed

drivers/md/raid1.c

+36 −56
Original line number Diff line number Diff line
@@ -419,11 +419,13 @@ static void raid1_end_write_request(struct bio *bio, int error) 
static int read_balance(conf_t *conf, r1bio_t *r1_bio)

{

	const sector_t this_sector = r1_bio->sector;

	int new_disk = conf->last_used, disk = new_disk;

	int wonly_disk = -1;

	const int sectors = r1_bio->sectors;

	int new_disk = -1;

	int start_disk;

	int i;

	sector_t new_distance, current_distance;

	mdk_rdev_t *rdev;

	int choose_first;



	rcu_read_lock();

	/*
@@ -434,54 +436,33 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 
 retry:

	if (conf->mddev->recovery_cp < MaxSector &&

	    (this_sector + sectors >= conf->next_resync)) {

		/* Choose the first operational device, for consistancy */

		new_disk = 0;



		for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);

		     r1_bio->bios[new_disk] == IO_BLOCKED ||

		     !rdev || !test_bit(In_sync, &rdev->flags)

			     || test_bit(WriteMostly, &rdev->flags);

		     rdev = rcu_dereference(conf->mirrors[++new_disk].rdev)) {



			if (rdev && test_bit(In_sync, &rdev->flags) &&

				r1_bio->bios[new_disk] != IO_BLOCKED)

				wonly_disk = new_disk;



			if (new_disk == conf->raid_disks - 1) {

				new_disk = wonly_disk;

				break;

			}

		}

		goto rb_out;

		choose_first = 1;

		start_disk = 0;

	} else {

		choose_first = 0;

		start_disk = conf->last_used;

	}





	/* make sure the disk is operational */

	for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);

	     r1_bio->bios[new_disk] == IO_BLOCKED ||

	     !rdev || !test_bit(In_sync, &rdev->flags) ||

		     test_bit(WriteMostly, &rdev->flags);

	     rdev = rcu_dereference(conf->mirrors[new_disk].rdev)) {



		if (rdev && test_bit(In_sync, &rdev->flags) &&

		    r1_bio->bios[new_disk] != IO_BLOCKED)

			wonly_disk = new_disk;



		if (new_disk <= 0)

			new_disk = conf->raid_disks;

		new_disk--;

		if (new_disk == disk) {

			new_disk = wonly_disk;

	for (i = 0 ; i < conf->raid_disks ; i++) {

		int disk = start_disk + i;

		if (disk >= conf->raid_disks)

			disk -= conf->raid_disks;



		rdev = rcu_dereference(conf->mirrors[disk].rdev);

		if (r1_bio->bios[disk] == IO_BLOCKED

		    || rdev == NULL

		    || !test_bit(In_sync, &rdev->flags))

			continue;



		new_disk = disk;

		if (!test_bit(WriteMostly, &rdev->flags))

			break;

	}

	}



	if (new_disk < 0)

	if (new_disk < 0 || choose_first)

		goto rb_out;



	disk = new_disk;

	/* now disk == new_disk == starting point for search */



	/*

	 * Don't change to another disk for sequential reads:

	 */
@@ -490,20 +471,21 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 
	if (this_sector == conf->mirrors[new_disk].head_position)

		goto rb_out;



	current_distance = abs(this_sector - conf->mirrors[disk].head_position);

	current_distance = abs(this_sector 

			       - conf->mirrors[new_disk].head_position);



	/* Find the disk whose head is closest */



	do {

		if (disk <= 0)

			disk = conf->raid_disks;

		disk--;

	/* look for a better disk - i.e. head is closer */

	start_disk = new_disk;

	for (i = 1; i < conf->raid_disks; i++) {

		int disk = start_disk + 1;

		if (disk >= conf->raid_disks)

			disk -= conf->raid_disks;



		rdev = rcu_dereference(conf->mirrors[disk].rdev);



		if (!rdev || r1_bio->bios[disk] == IO_BLOCKED ||

		    !test_bit(In_sync, &rdev->flags) ||

		    test_bit(WriteMostly, &rdev->flags))

		if (r1_bio->bios[disk] == IO_BLOCKED

		    || rdev == NULL

		    || !test_bit(In_sync, &rdev->flags)

		    || test_bit(WriteMostly, &rdev->flags))

			continue;



		if (!atomic_read(&rdev->nr_pending)) {
@@ -515,11 +497,9 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 
			current_distance = new_distance;

			new_disk = disk;

		}

	} while (disk != conf->last_used);

	}



 rb_out:





	if (new_disk >= 0) {

		rdev = rcu_dereference(conf->mirrors[new_disk].rdev);

		if (!rdev)