On 2012-07-04 13:22 Shaohua Li <shli@xxxxxxxxxx> Wrote:
>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@xxxxxxxxxxxx>
>---
> drivers/md/raid5.c | 35 +++++++++++++++++++----------------
> drivers/md/raid5.h | 1 +
> 2 files changed, 20 insertions(+), 16 deletions(-)
>
>Index: linux/drivers/md/raid5.c
>===================================================================
>--- linux.orig/drivers/md/raid5.c 2012-07-04 12:57:32.000000000 +0800
>+++ linux/drivers/md/raid5.c 2012-07-04 13:00:21.579462468 +0800
>@@ -755,14 +755,12 @@ static void ops_complete_biofill(void *s
> {
> 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];
>
>@@ -788,7 +786,6 @@ static void ops_complete_biofill(void *s
> }
> }
> }
>- spin_unlock_irq(&conf->device_lock);
> clear_bit(STRIPE_BIOFILL_RUN, &sh->state);
>
> return_io(return_bi);
>@@ -800,7 +797,6 @@ static void ops_complete_biofill(void *s
> 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;
>
>@@ -811,10 +807,10 @@ static void ops_run_biofill(struct strip
> 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,
>@@ -1150,12 +1146,12 @@ ops_run_biodrain(struct stripe_head *sh,
> 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) {
>@@ -1460,6 +1456,8 @@ static int grow_one_stripe(struct r5conf
> 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);
>@@ -2346,8 +2344,15 @@ static int add_stripe_bio(struct stripe_
> (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)
>@@ -2381,7 +2386,7 @@ static int add_stripe_bio(struct stripe_
> 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,
>@@ -2397,7 +2402,7 @@ static int add_stripe_bio(struct stripe_
>
> overlap:
> set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
>- spin_unlock_irq(&conf->device_lock);
>+ spin_unlock_irq(&sh->stripe_lock);
> return 0;
> }
>
>@@ -2447,7 +2452,7 @@ handle_failed_stripe(struct r5conf *conf
> 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;
>@@ -2455,7 +2460,7 @@ handle_failed_stripe(struct r5conf *conf
> s->to_write--;
> bitmap_end = 1;
> }
>- spin_unlock_irq(&conf->device_lock);
>+ spin_unlock_irq(&sh->stripe_lock);
>
> if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
> wake_up(&conf->wait_for_overlap);
>@@ -3185,7 +3190,6 @@ static void analyse_stripe(struct stripe
>
> /* 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;
>@@ -3331,7 +3335,6 @@ static void analyse_stripe(struct stripe
> 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.
>Index: linux/drivers/md/raid5.h
>===================================================================
>--- linux.orig/drivers/md/raid5.h 2012-07-04 12:15:38.000000000 +0800
>+++ linux/drivers/md/raid5.h 2012-07-04 12:58:46.412659090 +0800
>@@ -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
>--
If dev/stripe was overwrite or overread, add_stripe_bio and ops_run_biofill/biodrain will not race.
If it is, it can be optimized.?韬{.n?????%??檩??w?{.n???{炳盯w???塄}?财??j:+v?? ? ???2??璀??摺?囤??z夸z罐?+?????w棹f
