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Commit 8ddf9efe authored by NeilBrown's avatar NeilBrown Committed by Linus Torvalds
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[PATCH] md: support write-mostly device in raid1 



This allows a device in a raid1 to be marked as "write mostly".  Read requests
will only be sent if there is no other option.

Signed-off-by: default avatarNeil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 36fa3063

drivers/md/md.c

+18 −0
Original line number Diff line number Diff line
@@ -670,6 +670,7 @@ static int super_90_validate(mddev_t *mddev, mdk_rdev_t *rdev) 


	if (mddev->level != LEVEL_MULTIPATH) {

		rdev->faulty = 0;

		rdev->flags = 0;

		desc = sb->disks + rdev->desc_nr;



		if (desc->state & (1<<MD_DISK_FAULTY))
@@ -679,6 +680,8 @@ static int super_90_validate(mddev_t *mddev, mdk_rdev_t *rdev) 
			rdev->in_sync = 1;

			rdev->raid_disk = desc->raid_disk;

		}

		if (desc->state & (1<<MD_DISK_WRITEMOSTLY))

			set_bit(WriteMostly, &rdev->flags);

	} else /* MULTIPATH are always insync */

		rdev->in_sync = 1;

	return 0;
@@ -777,6 +780,8 @@ static void super_90_sync(mddev_t *mddev, mdk_rdev_t *rdev) 
			spare++;

			working++;

		}

		if (test_bit(WriteMostly, &rdev2->flags))

			d->state |= (1<<MD_DISK_WRITEMOSTLY);

	}

	

	/* now set the "removed" and "faulty" bits on any missing devices */
@@ -990,6 +995,9 @@ static int super_1_validate(mddev_t *mddev, mdk_rdev_t *rdev) 
			rdev->raid_disk = role;

			break;

		}

		rdev->flags = 0;

		if (sb->devflags & WriteMostly1)

			set_bit(WriteMostly, &rdev->flags);

	} else /* MULTIPATH are always insync */

		rdev->in_sync = 1;
@@ -2152,6 +2160,8 @@ static int get_disk_info(mddev_t * mddev, void __user * arg) 
			info.state |= (1<<MD_DISK_ACTIVE);

			info.state |= (1<<MD_DISK_SYNC);

		}

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

			info.state |= (1<<MD_DISK_WRITEMOSTLY);

	} else {

		info.major = info.minor = 0;

		info.raid_disk = -1;
@@ -2237,6 +2247,9 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info) 
		rdev->saved_raid_disk = rdev->raid_disk;



		rdev->in_sync = 0; /* just to be sure */

		if (info->state & (1<<MD_DISK_WRITEMOSTLY))

			set_bit(WriteMostly, &rdev->flags);



		rdev->raid_disk = -1;

		err = bind_rdev_to_array(rdev, mddev);

		if (err)
@@ -2277,6 +2290,9 @@ static int add_new_disk(mddev_t * mddev, mdu_disk_info_t *info) 
		else

			rdev->in_sync = 0;



		if (info->state & (1<<MD_DISK_WRITEMOSTLY))

			set_bit(WriteMostly, &rdev->flags);



		err = bind_rdev_to_array(rdev, mddev);

		if (err) {

			export_rdev(rdev);
@@ -3329,6 +3345,8 @@ static int md_seq_show(struct seq_file *seq, void *v) 
			char b[BDEVNAME_SIZE];

			seq_printf(seq, " %s[%d]",

				bdevname(rdev->bdev,b), rdev->desc_nr);

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

				seq_printf(seq, "(W)");

			if (rdev->faulty) {

				seq_printf(seq, "(F)");

				continue;

drivers/md/raid1.c

+52 −24
Original line number Diff line number Diff line
@@ -360,13 +360,14 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 
{

	const unsigned long this_sector = r1_bio->sector;

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

	int wonly_disk = -1;

	const int sectors = r1_bio->sectors;

	sector_t new_distance, current_distance;

	mdk_rdev_t *new_rdev, *rdev;

	mdk_rdev_t *rdev;



	rcu_read_lock();

	/*

	 * Check if it if we can balance. We can balance on the whole

	 * Check if we can balance. We can balance on the whole

	 * device if no resync is going on, or below the resync window.

	 * We take the first readable disk when above the resync window.

	 */
@@ -376,11 +377,16 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 
		/* Choose the first operation device, for consistancy */

		new_disk = 0;



		while ((new_rdev=conf->mirrors[new_disk].rdev) == NULL ||

		       !new_rdev->in_sync) {

			new_disk++;

			if (new_disk == conf->raid_disks) {

				new_disk = -1;

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

		     !rdev || !rdev->in_sync

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

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



			if (rdev && rdev->in_sync)

				wonly_disk = new_disk;



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

				new_disk = wonly_disk;

				break;

			}

		}
@@ -389,16 +395,26 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 




	/* make sure the disk is operational */

	while ((new_rdev=conf->mirrors[new_disk].rdev) == NULL ||

	       !new_rdev->in_sync) {

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

	     !rdev || !rdev->in_sync ||

		     test_bit(WriteMostly, &rdev->flags);

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



		if (rdev && rdev->in_sync)

			wonly_disk = new_disk;



		if (new_disk <= 0)

			new_disk = conf->raid_disks;

		new_disk--;

		if (new_disk == disk) {

			new_disk = -1;

			goto rb_out;

			new_disk = wonly_disk;

			break;

		}

	}



	if (new_disk < 0)

		goto rb_out;



	disk = new_disk;

	/* now disk == new_disk == starting point for search */
@@ -419,20 +435,21 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) 
			disk = conf->raid_disks;

		disk--;



		if ((rdev=conf->mirrors[disk].rdev) == NULL ||

		    !rdev->in_sync)

		rdev = conf->mirrors[disk].rdev;



		if (!rdev ||

		    !rdev->in_sync ||

		    test_bit(WriteMostly, &rdev->flags))

			continue;



		if (!atomic_read(&rdev->nr_pending)) {

			new_disk = disk;

			new_rdev = rdev;

			break;

		}

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

		if (new_distance < current_distance) {

			current_distance = new_distance;

			new_disk = disk;

			new_rdev = rdev;

		}

	} while (disk != conf->last_used);
@@ -440,16 +457,19 @@ rb_out: 




	if (new_disk >= 0) {

		conf->next_seq_sect = this_sector + sectors;

		conf->last_used = new_disk;

		atomic_inc(&new_rdev->nr_pending);

		if (!new_rdev->in_sync) {

		rdev = conf->mirrors[new_disk].rdev;

		if (!rdev)

			goto retry;

		atomic_inc(&rdev->nr_pending);

		if (!rdev->in_sync) {

			/* cannot risk returning a device that failed

			 * before we inc'ed nr_pending

			 */

			atomic_dec(&new_rdev->nr_pending);

			atomic_dec(&rdev->nr_pending);

			goto retry;

		}

		conf->next_seq_sect = this_sector + sectors;

		conf->last_used = new_disk;

	}

	rcu_read_unlock();
@@ -1109,6 +1129,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i 
	sector_t max_sector, nr_sectors;

	int disk;

	int i;

	int wonly;

	int write_targets = 0;

	int sync_blocks;

	int still_degraded = 0;
@@ -1164,15 +1185,22 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i 
	 */

	disk = conf->last_used;

	/* make sure disk is operational */



	wonly = disk;

	while (conf->mirrors[disk].rdev == NULL ||

	       !conf->mirrors[disk].rdev->in_sync) {

	       !conf->mirrors[disk].rdev->in_sync ||

	       test_bit(WriteMostly, &conf->mirrors[disk].rdev->flags)

		) {

		if (conf->mirrors[disk].rdev  &&

		    conf->mirrors[disk].rdev->in_sync)

			wonly = disk;

		if (disk <= 0)

			disk = conf->raid_disks;

		disk--;

		if (disk == conf->last_used)

		if (disk == conf->last_used) {

			disk = wonly;

			break;

		}

	}

	conf->last_used = disk;

	atomic_inc(&conf->mirrors[disk].rdev->nr_pending);

include/linux/raid/md_k.h

+3 −0
Original line number Diff line number Diff line
@@ -181,6 +181,9 @@ struct mdk_rdev_s 
	int faulty;			/* if faulty do not issue IO requests */

	int in_sync;			/* device is a full member of the array */



	unsigned long	flags;		/* Should include faulty and in_sync here. */

#define	WriteMostly	4		/* Avoid reading if at all possible */



	int desc_nr;			/* descriptor index in the superblock */

	int raid_disk;			/* role of device in array */

	int saved_raid_disk;		/* role that device used to have in the

include/linux/raid/md_p.h

+9 −2
Original line number Diff line number Diff line
@@ -79,6 +79,11 @@ 
#define MD_DISK_SYNC		2 /* disk is in sync with the raid set */

#define MD_DISK_REMOVED		3 /* disk is in sync with the raid set */



#define	MD_DISK_WRITEMOSTLY	9 /* disk is "write-mostly" is RAID1 config.

				   * read requests will only be sent here in

				   * dire need

				   */



typedef struct mdp_device_descriptor_s {

	__u32 number;		/* 0 Device number in the entire set	      */

	__u32 major;		/* 1 Device major number		      */
@@ -193,7 +198,7 @@ struct mdp_superblock_1 { 


	__u64	ctime;		/* lo 40 bits are seconds, top 24 are microseconds or 0*/

	__u32	level;		/* -4 (multipath), -1 (linear), 0,1,4,5 */

	__u32	layout;		/* only for raid5 currently */

	__u32	layout;		/* only for raid5 and raid10 currently */

	__u64	size;		/* used size of component devices, in 512byte sectors */



	__u32	chunksize;	/* in 512byte sectors */
@@ -212,7 +217,9 @@ struct mdp_superblock_1 { 
	__u32	dev_number;	/* permanent identifier of this  device - not role in raid */

	__u32	cnt_corrected_read; /* number of read errors that were corrected by re-writing */

	__u8	device_uuid[16]; /* user-space setable, ignored by kernel */

	__u8	pad2[64-56];	/* set to 0 when writing */

	__u8	devflags;	/* per-device flags.  Only one defined...*/

#define	WriteMostly1	1	/* mask for writemostly flag in above */

	__u8	pad2[64-57];	/* set to 0 when writing */



	/* array state information - 64 bytes */

	__u64	utime;		/* 40 bits second, 24 btes microseconds */