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[PATCH] md: add write-intent-bitmap support to raid5
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Most awkward part of this is delaying write requests until bitmap updates have
been flushed.

To achieve this, we have a sequence number (seq_flush) which is incremented
each time the raid5 is unplugged.

If the raid thread notices that this has changed, it flushes bitmap changes,
and assigned the value of seq_flush to seq_write.

When a write request arrives, it is given the number from seq_write, and that
write request may not complete until seq_flush is larger than the saved seq
number.

We have a new queue for storing stripes which are waiting for a bitmap flush
and an extra flag for stripes to record if the write was 'degraded' and so
should not clear the a bit in the bitmap.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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NeilBrown authored and Linus Torvalds committed Sep 9, 2005
1 parent 0002b27 commit 7262668
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Showing 3 changed files with 137 additions and 13 deletions.
3 changes: 1 addition & 2 deletions drivers/md/md.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -645,7 +645,7 @@ static int super_90_validate(mddev_t *mddev, mdk_rdev_t *rdev)

if (sb->state & (1<<MD_SB_BITMAP_PRESENT) &&
mddev->bitmap_file == NULL) {
if (mddev->level != 1) {
if (mddev->level != 1 && mddev->level != 5) {
/* FIXME use a better test */
printk(KERN_WARNING "md: bitmaps only support for raid1\n");
return -EINVAL;
Expand Down Expand Up @@ -3517,7 +3517,6 @@ void md_done_sync(mddev_t *mddev, int blocks, int ok)
*/
void md_write_start(mddev_t *mddev, struct bio *bi)
{
DEFINE_WAIT(w);
if (bio_data_dir(bi) != WRITE)
return;

Expand Down
133 changes: 123 additions & 10 deletions drivers/md/raid5.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,8 @@
#include <linux/bitops.h>
#include <asm/atomic.h>

#include <linux/raid/bitmap.h>

/*
* Stripe cache
*/
Expand Down Expand Up @@ -79,8 +81,13 @@ static inline void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
if (test_bit(STRIPE_HANDLE, &sh->state)) {
if (test_bit(STRIPE_DELAYED, &sh->state))
list_add_tail(&sh->lru, &conf->delayed_list);
else
else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
conf->seq_write == sh->bm_seq)
list_add_tail(&sh->lru, &conf->bitmap_list);
else {
clear_bit(STRIPE_BIT_DELAY, &sh->state);
list_add_tail(&sh->lru, &conf->handle_list);
}
md_wakeup_thread(conf->mddev->thread);
} else {
if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
Expand Down Expand Up @@ -244,6 +251,9 @@ static struct stripe_head *get_active_stripe(raid5_conf_t *conf, sector_t sector
spin_lock_irq(&conf->device_lock);

do {
wait_event_lock_irq(conf->wait_for_stripe,
conf->quiesce == 0,
conf->device_lock, /* nothing */);
sh = __find_stripe(conf, sector);
if (!sh) {
if (!conf->inactive_blocked)
Expand Down Expand Up @@ -803,6 +813,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
{
struct bio **bip;
raid5_conf_t *conf = sh->raid_conf;
int firstwrite=0;

PRINTK("adding bh b#%llu to stripe s#%llu\n",
(unsigned long long)bi->bi_sector,
Expand All @@ -811,9 +822,11 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in

spin_lock(&sh->lock);
spin_lock_irq(&conf->device_lock);
if (forwrite)
if (forwrite) {
bip = &sh->dev[dd_idx].towrite;
else
if (*bip == NULL && sh->dev[dd_idx].written == NULL)
firstwrite = 1;
} else
bip = &sh->dev[dd_idx].toread;
while (*bip && (*bip)->bi_sector < bi->bi_sector) {
if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
Expand All @@ -836,6 +849,13 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
(unsigned long long)bi->bi_sector,
(unsigned long long)sh->sector, dd_idx);

if (conf->mddev->bitmap && firstwrite) {
sh->bm_seq = conf->seq_write;
bitmap_startwrite(conf->mddev->bitmap, sh->sector,
STRIPE_SECTORS, 0);
set_bit(STRIPE_BIT_DELAY, &sh->state);
}

if (forwrite) {
/* check if page is covered */
sector_t sector = sh->dev[dd_idx].sector;
Expand Down Expand Up @@ -958,12 +978,13 @@ static void handle_stripe(struct stripe_head *sh)
* need to be failed
*/
if (failed > 1 && to_read+to_write+written) {
spin_lock_irq(&conf->device_lock);
for (i=disks; i--; ) {
int bitmap_end = 0;
spin_lock_irq(&conf->device_lock);
/* fail all writes first */
bi = sh->dev[i].towrite;
sh->dev[i].towrite = NULL;
if (bi) to_write--;
if (bi) { to_write--; bitmap_end = 1; }

if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
wake_up(&conf->wait_for_overlap);
Expand All @@ -981,6 +1002,7 @@ static void handle_stripe(struct stripe_head *sh)
/* and fail all 'written' */
bi = sh->dev[i].written;
sh->dev[i].written = NULL;
if (bi) bitmap_end = 1;
while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS) {
struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
clear_bit(BIO_UPTODATE, &bi->bi_flags);
Expand Down Expand Up @@ -1009,8 +1031,11 @@ static void handle_stripe(struct stripe_head *sh)
bi = nextbi;
}
}
spin_unlock_irq(&conf->device_lock);
if (bitmap_end)
bitmap_endwrite(conf->mddev->bitmap, sh->sector,
STRIPE_SECTORS, 0, 0);
}
spin_unlock_irq(&conf->device_lock);
}
if (failed > 1 && syncing) {
md_done_sync(conf->mddev, STRIPE_SECTORS,0);
Expand Down Expand Up @@ -1038,6 +1063,7 @@ static void handle_stripe(struct stripe_head *sh)
test_bit(R5_UPTODATE, &dev->flags) ) {
/* We can return any write requests */
struct bio *wbi, *wbi2;
int bitmap_end = 0;
PRINTK("Return write for disc %d\n", i);
spin_lock_irq(&conf->device_lock);
wbi = dev->written;
Expand All @@ -1051,7 +1077,13 @@ static void handle_stripe(struct stripe_head *sh)
}
wbi = wbi2;
}
if (dev->towrite == NULL)
bitmap_end = 1;
spin_unlock_irq(&conf->device_lock);
if (bitmap_end)
bitmap_endwrite(conf->mddev->bitmap, sh->sector,
STRIPE_SECTORS,
!test_bit(STRIPE_DEGRADED, &sh->state), 0);
}
}
}
Expand Down Expand Up @@ -1175,7 +1207,8 @@ static void handle_stripe(struct stripe_head *sh)
}
}
/* now if nothing is locked, and if we have enough data, we can start a write request */
if (locked == 0 && (rcw == 0 ||rmw == 0)) {
if (locked == 0 && (rcw == 0 ||rmw == 0) &&
!test_bit(STRIPE_BIT_DELAY, &sh->state)) {
PRINTK("Computing parity...\n");
compute_parity(sh, rcw==0 ? RECONSTRUCT_WRITE : READ_MODIFY_WRITE);
/* now every locked buffer is ready to be written */
Expand Down Expand Up @@ -1231,6 +1264,7 @@ static void handle_stripe(struct stripe_head *sh)
dev = &sh->dev[failed_num];
set_bit(R5_LOCKED, &dev->flags);
set_bit(R5_Wantwrite, &dev->flags);
clear_bit(STRIPE_DEGRADED, &sh->state);
locked++;
set_bit(STRIPE_INSYNC, &sh->state);
set_bit(R5_Syncio, &dev->flags);
Expand Down Expand Up @@ -1298,6 +1332,8 @@ static void handle_stripe(struct stripe_head *sh)
bi->bi_next = NULL;
generic_make_request(bi);
} else {
if (rw == 1)
set_bit(STRIPE_DEGRADED, &sh->state);
PRINTK("skip op %ld on disc %d for sector %llu\n",
bi->bi_rw, i, (unsigned long long)sh->sector);
clear_bit(R5_LOCKED, &sh->dev[i].flags);
Expand All @@ -1322,6 +1358,20 @@ static inline void raid5_activate_delayed(raid5_conf_t *conf)
}
}

static inline void activate_bit_delay(raid5_conf_t *conf)
{
/* device_lock is held */
struct list_head head;
list_add(&head, &conf->bitmap_list);
list_del_init(&conf->bitmap_list);
while (!list_empty(&head)) {
struct stripe_head *sh = list_entry(head.next, struct stripe_head, lru);
list_del_init(&sh->lru);
atomic_inc(&sh->count);
__release_stripe(conf, sh);
}
}

static void unplug_slaves(mddev_t *mddev)
{
raid5_conf_t *conf = mddev_to_conf(mddev);
Expand Down Expand Up @@ -1354,8 +1404,10 @@ static void raid5_unplug_device(request_queue_t *q)

spin_lock_irqsave(&conf->device_lock, flags);

if (blk_remove_plug(q))
if (blk_remove_plug(q)) {
conf->seq_flush++;
raid5_activate_delayed(conf);
}
md_wakeup_thread(mddev->thread);

spin_unlock_irqrestore(&conf->device_lock, flags);
Expand Down Expand Up @@ -1493,10 +1545,20 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
sector_t first_sector;
int raid_disks = conf->raid_disks;
int data_disks = raid_disks-1;
sector_t max_sector = mddev->size << 1;
int sync_blocks;

if (sector_nr >= mddev->size <<1) {
if (sector_nr >= max_sector) {
/* just being told to finish up .. nothing much to do */
unplug_slaves(mddev);

if (mddev->curr_resync < max_sector) /* aborted */
bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
&sync_blocks, 1);
else /* compelted sync */
conf->fullsync = 0;
bitmap_close_sync(mddev->bitmap);

return 0;
}
/* if there is 1 or more failed drives and we are trying
Expand All @@ -1508,6 +1570,13 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
*skipped = 1;
return rv;
}
if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
!conf->fullsync && sync_blocks >= STRIPE_SECTORS) {
/* we can skip this block, and probably more */
sync_blocks /= STRIPE_SECTORS;
*skipped = 1;
return sync_blocks * STRIPE_SECTORS; /* keep things rounded to whole stripes */
}

x = sector_nr;
chunk_offset = sector_div(x, sectors_per_chunk);
Expand All @@ -1525,6 +1594,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
set_current_state(TASK_UNINTERRUPTIBLE);
schedule_timeout(1);
}
bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 0);
spin_lock(&sh->lock);
set_bit(STRIPE_SYNCING, &sh->state);
clear_bit(STRIPE_INSYNC, &sh->state);
Expand Down Expand Up @@ -1558,6 +1628,13 @@ static void raid5d (mddev_t *mddev)
while (1) {
struct list_head *first;

if (conf->seq_flush - conf->seq_write > 0) {
int seq = conf->seq_flush;
bitmap_unplug(mddev->bitmap);
conf->seq_write = seq;
activate_bit_delay(conf);
}

if (list_empty(&conf->handle_list) &&
atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD &&
!blk_queue_plugged(mddev->queue) &&
Expand Down Expand Up @@ -1591,7 +1668,7 @@ static void raid5d (mddev_t *mddev)
PRINTK("--- raid5d inactive\n");
}

static int run (mddev_t *mddev)
static int run(mddev_t *mddev)
{
raid5_conf_t *conf;
int raid_disk, memory;
Expand Down Expand Up @@ -1621,6 +1698,7 @@ static int run (mddev_t *mddev)
init_waitqueue_head(&conf->wait_for_overlap);
INIT_LIST_HEAD(&conf->handle_list);
INIT_LIST_HEAD(&conf->delayed_list);
INIT_LIST_HEAD(&conf->bitmap_list);
INIT_LIST_HEAD(&conf->inactive_list);
atomic_set(&conf->active_stripes, 0);
atomic_set(&conf->preread_active_stripes, 0);
Expand Down Expand Up @@ -1732,6 +1810,9 @@ memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +

/* Ok, everything is just fine now */

if (mddev->bitmap)
mddev->thread->timeout = mddev->bitmap->daemon_sleep * HZ;

mddev->queue->unplug_fn = raid5_unplug_device;
mddev->queue->issue_flush_fn = raid5_issue_flush;

Expand Down Expand Up @@ -1912,6 +1993,8 @@ static int raid5_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
rdev->in_sync = 0;
rdev->raid_disk = disk;
found = 1;
if (rdev->saved_raid_disk != disk)
conf->fullsync = 1;
p->rdev = rdev;
break;
}
Expand Down Expand Up @@ -1941,6 +2024,35 @@ static int raid5_resize(mddev_t *mddev, sector_t sectors)
return 0;
}

static void raid5_quiesce(mddev_t *mddev, int state)
{
raid5_conf_t *conf = mddev_to_conf(mddev);

switch(state) {
case 1: /* stop all writes */
spin_lock_irq(&conf->device_lock);
conf->quiesce = 1;
wait_event_lock_irq(conf->wait_for_stripe,
atomic_read(&conf->active_stripes) == 0,
conf->device_lock, /* nothing */);
spin_unlock_irq(&conf->device_lock);
break;

case 0: /* re-enable writes */
spin_lock_irq(&conf->device_lock);
conf->quiesce = 0;
wake_up(&conf->wait_for_stripe);
spin_unlock_irq(&conf->device_lock);
break;
}
if (mddev->thread) {
if (mddev->bitmap)
mddev->thread->timeout = mddev->bitmap->daemon_sleep * HZ;
else
mddev->thread->timeout = MAX_SCHEDULE_TIMEOUT;
md_wakeup_thread(mddev->thread);
}
}
static mdk_personality_t raid5_personality=
{
.name = "raid5",
Expand All @@ -1955,6 +2067,7 @@ static mdk_personality_t raid5_personality=
.spare_active = raid5_spare_active,
.sync_request = sync_request,
.resize = raid5_resize,
.quiesce = raid5_quiesce,
};

static int __init raid5_init (void)
Expand Down
14 changes: 13 additions & 1 deletion include/linux/raid/raid5.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -134,6 +134,7 @@ struct stripe_head {
unsigned long state; /* state flags */
atomic_t count; /* nr of active thread/requests */
spinlock_t lock;
int bm_seq; /* sequence number for bitmap flushes */
struct r5dev {
struct bio req;
struct bio_vec vec;
Expand Down Expand Up @@ -165,12 +166,13 @@ struct stripe_head {
/*
* Stripe state
*/
#define STRIPE_ERROR 1
#define STRIPE_HANDLE 2
#define STRIPE_SYNCING 3
#define STRIPE_INSYNC 4
#define STRIPE_PREREAD_ACTIVE 5
#define STRIPE_DELAYED 6
#define STRIPE_DEGRADED 7
#define STRIPE_BIT_DELAY 8

/*
* Plugging:
Expand Down Expand Up @@ -210,10 +212,20 @@ struct raid5_private_data {

struct list_head handle_list; /* stripes needing handling */
struct list_head delayed_list; /* stripes that have plugged requests */
struct list_head bitmap_list; /* stripes delaying awaiting bitmap update */
atomic_t preread_active_stripes; /* stripes with scheduled io */

char cache_name[20];
kmem_cache_t *slab_cache; /* for allocating stripes */

int seq_flush, seq_write;
int quiesce;

int fullsync; /* set to 1 if a full sync is needed,
* (fresh device added).
* Cleared when a sync completes.
*/

/*
* Free stripes pool
*/
Expand Down

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