From b17459c05000fdbe8d10946570a26510f86ec0f6 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Thu, 19 Jul 2012 16:01:31 +1000 Subject: 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 Signed-off-by: NeilBrown --- drivers/md/raid5.c | 35 +++++++++++++++++++---------------- drivers/md/raid5.h | 1 + 2 files changed, 20 insertions(+), 16 deletions(-) (limited to 'drivers/md') diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 9ad452c6d7e3..c2192a2907e4 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -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. diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h index 2164021f3b5f..f03fb3395183 100644 --- a/drivers/md/raid5.h +++ b/drivers/md/raid5.h @@ -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 -- cgit v1.2.3-55-g7522