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raid5: add a per-stripe lock 

Add a per-stripe lock to protect stripe specific data. The purpose is to reduce
lock contention of conf->device_lock.

stripe ->toread, ->towrite are protected by per-stripe lock.  Accessing bio
list of the stripe is always serialized by this lock, so adding bio to the
lists (add_stripe_bio()) and removing bio from the lists (like
ops_run_biofill()) not race.

If bio in ->read, ->written ... list are not shared by multiple stripes, we
don't need any lock to protect ->read, ->written, because STRIPE_ACTIVE will
protect them. If the bio are shared,  there are two protections:
1. bi_phys_segments acts as a reference count
2. traverse the list uses r5_next_bio, which makes traverse never access bio
not belonging to the stripe

Let's have an example:
|  stripe1 |  stripe2    |  stripe3  |
...bio1......|bio2|bio3|....bio4.....

stripe2 has 4 bios, when it's finished, it will decrement bi_phys_segments for
all bios, but only end_bio for bio2 and bio3. bio1->bi_next still points to
bio2, but this doesn't matter. When stripe1 is finished, it will not touch bio2
because of r5_next_bio check. Next time stripe1 will end_bio for bio1 and
stripe3 will end_bio bio4.

before add_stripe_bio() addes a bio to a stripe, we already increament the bio
bi_phys_segments, so don't worry other stripes release the bio.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
Shaohua Li 2012-07-19 16:01:31 +10:00 committed by NeilBrown
parent 7eaf7e8eb3
commit b17459c050
2 changed files with 20 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
drivers/md/raid5.c
View File

@ -762,14 +762,12 @@ static void ops_complete_biofill(void *stripe_head_ref)
{
struct stripe_head *sh = stripe_head_ref;
struct bio *return_bi = NULL;
struct r5conf *conf = sh->raid_conf;
int i;
pr_debug("%s: stripe %llu\n", __func__,
(unsigned long long)sh->sector);
/* clear completed biofills */
spin_lock_irq(&conf->device_lock);
for (i = sh->disks; i--; ) {
struct r5dev *dev = &sh->dev[i];
@ -795,7 +793,6 @@ static void ops_complete_biofill(void *stripe_head_ref)
}
}
}
spin_unlock_irq(&conf->device_lock);
clear_bit(STRIPE_BIOFILL_RUN, &sh->state);
return_io(return_bi);
@ -807,7 +804,6 @@ static void ops_complete_biofill(void *stripe_head_ref)
static void ops_run_biofill(struct stripe_head *sh)
{
struct dma_async_tx_descriptor *tx = NULL;
struct r5conf *conf = sh->raid_conf;
struct async_submit_ctl submit;
int i;
@ -818,10 +814,10 @@ static void ops_run_biofill(struct stripe_head *sh)
struct r5dev *dev = &sh->dev[i];
if (test_bit(R5_Wantfill, &dev->flags)) {
struct bio *rbi;
spin_lock_irq(&conf->device_lock);
spin_lock_irq(&sh->stripe_lock);
dev->read = rbi = dev->toread;
dev->toread = NULL;
spin_unlock_irq(&conf->device_lock);
spin_unlock_irq(&sh->stripe_lock);
while (rbi && rbi->bi_sector <
dev->sector + STRIPE_SECTORS) {
tx = async_copy_data(0, rbi, dev->page,
@ -1157,12 +1153,12 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {
struct bio *wbi;
spin_lock_irq(&sh->raid_conf->device_lock);
spin_lock_irq(&sh->stripe_lock);
chosen = dev->towrite;
dev->towrite = NULL;
BUG_ON(dev->written);
wbi = dev->written = chosen;
spin_unlock_irq(&sh->raid_conf->device_lock);
spin_unlock_irq(&sh->stripe_lock);
while (wbi && wbi->bi_sector <
dev->sector + STRIPE_SECTORS) {
@ -1467,6 +1463,8 @@ static int grow_one_stripe(struct r5conf *conf)
init_waitqueue_head(&sh->ops.wait_for_ops);
#endif
spin_lock_init(&sh->stripe_lock);
if (grow_buffers(sh)) {
shrink_buffers(sh);
kmem_cache_free(conf->slab_cache, sh);
@ -2353,8 +2351,15 @@ 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);
spin_lock_irq(&conf->device_lock);
/*
* If several bio share a stripe. The bio bi_phys_segments acts as a
* reference count to avoid race. The reference count should already be
* increased before this function is called (for example, in
* make_request()), so other bio sharing this stripe will not free the
* stripe. If a stripe is owned by one stripe, the stripe lock will
* protect it.
*/
spin_lock_irq(&sh->stripe_lock);
if (forwrite) {
bip = &sh->dev[dd_idx].towrite;
if (*bip == NULL)
@ -2388,7 +2393,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
}
spin_unlock_irq(&conf->device_lock);
spin_unlock_irq(&sh->stripe_lock);
pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
(unsigned long long)(*bip)->bi_sector,
@ -2404,7 +2409,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
overlap:
set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
spin_unlock_irq(&conf->device_lock);
spin_unlock_irq(&sh->stripe_lock);
return 0;
}
@ -2454,11 +2459,11 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
rdev_dec_pending(rdev, conf->mddev);
}
}
spin_lock_irq(&conf->device_lock);
spin_lock_irq(&sh->stripe_lock);
/* fail all writes first */
bi = sh->dev[i].towrite;
sh->dev[i].towrite = NULL;
spin_unlock_irq(&conf->device_lock);
spin_unlock_irq(&sh->stripe_lock);
if (bi) {
s->to_write--;
bitmap_end = 1;
@ -3192,7 +3197,6 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
/* Now to look around and see what can be done */
rcu_read_lock();
spin_lock_irq(&conf->device_lock);
for (i=disks; i--; ) {
struct md_rdev *rdev;
sector_t first_bad;
@ -3338,7 +3342,6 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
do_recovery = 1;
}
}
spin_unlock_irq(&conf->device_lock);
if (test_bit(STRIPE_SYNCING, &sh->state)) {
/* If there is a failed device being replaced,
* we must be recovering.

1
drivers/md/raid5.h
View File

@ -210,6 +210,7 @@ struct stripe_head {
int disks; /* disks in stripe */
enum check_states check_state;
enum reconstruct_states reconstruct_state;
spinlock_t stripe_lock;
/**
* struct stripe_operations
* @target - STRIPE_OP_COMPUTE_BLK target