On Thu, Sep 05, 2013 at 04:29:10PM +1000, NeilBrown wrote:
> On Thu, 5 Sep 2013 13:40:35 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote:
>
> > On Wed, Sep 04, 2013 at 04:41:32PM +1000, NeilBrown wrote:
> > > On Tue, 3 Sep 2013 15:02:28 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote:
> > >
> > > > On Tue, Sep 03, 2013 at 04:08:58PM +1000, NeilBrown wrote:
> > > > > On Wed, 28 Aug 2013 14:39:53 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote:
> > > > >
> > > > > > On Wed, Aug 28, 2013 at 02:32:52PM +1000, NeilBrown wrote:
> > > > > > > On Tue, 27 Aug 2013 16:53:30 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > > On Tue, Aug 27, 2013 at 01:17:52PM +1000, NeilBrown wrote:
> > > > > > >
> > > > > > > >
> > > > > > > > > Then get_active_stripe wouldn't need to worry about device_lock at all and
> > > > > > > > > would only need to get the hash lock for the particular sector. That should
> > > > > > > > > make it a lot simpler.
> > > > > > > >
> > > > > > > > did you mean get_active_stripe() doesn't need device_lock for any code path?
> > > > > > > > How could it be safe? device_lock still protects something like handle_list,
> > > > > > > > delayed_list, which release_stripe() will use while a get_active_stripe can run
> > > > > > > > concurrently.
> > > > > > >
> > > > > > > Yes you will still need device_lock to protect list_del_init(&sh->lru),
> > > > > > > as well as the hash lock.
> > > > > > > Do you need device_lock anywhere else in there?
> > > > > >
> > > > > > That's what I mean. So I need get both device_lock and hash_lock. To not
> > > > > > deadlock, I need release hash_lock and relock device_lock/hash_lock. Since I
> > > > > > release lock, I need recheck if I can find the stripe in hash again. So the
> > > > > > seqcount locking doesn't simplify things here. I thought the seqlock only fixes
> > > > > > one race. Did I miss anything?
> > > > >
> > > > > Can you order the locks so that you take the hash_lock first, then the
> > > > > device_lock? That would be a lot simpler.
> > > >
> > > > Looks impossible. For example, in handle_active_stripes() we release several
> > > > stripes, we can't take hash_lock first.
> > >
> > > "impossible" just takes a little longer :-)
> > >
> > > do_release_stripe gets called with only device_lock held. It gets passed an
> > > (initially) empty list_head too.
> > > If it wants to add the stripe to an inactive list it puts it on the given
> > > list_head instead.
> > >
> > > release_stripe(), after calling do_release_stripe() calls some function to
> > > grab the appropriate hash_lock for each stripe in the list_head and add it
> > > to that inactive list.
> > >
> > > release_stripe_list() might collect some stripes from from __release_stripe
> > > that need to go on an inactive list. It arranges for them to be put on the
> > > right list, with the right lock, next time device_lock is dropped. That
> > > might be in handle_active_stripes()
> > >
> > > activate_bit_delay might similarly collect stripes, which are handled the
> > > same way as those collected by release_stripe_list.
> > > etc.
> > >
> > > i.e. the hash_locks protect the various inactive lists. device_lock protects
> > > all the others. If we need to add something to an inactive list while
> > > holding device_lock we delay until device_lock can be dropped.
> >
> > Alright, this option works, but we need allocate some spaces, which isn't very
> > good for unplug cb. Below is the patch I tested.
> >
> > Thanks,
> > Shaohua
> >
> > Subject: raid5: relieve lock contention in get_active_stripe()
> >
> > get_active_stripe() is the last place we have lock contention. It has two
> > paths. One is stripe isn't found and new stripe is allocated, the other is
> > stripe is found.
> >
> > The first path basically calls __find_stripe and init_stripe. It accesses
> > conf->generation, conf->previous_raid_disks, conf->raid_disks,
> > conf->prev_chunk_sectors, conf->chunk_sectors, conf->max_degraded,
> > conf->prev_algo, conf->algorithm, the stripe_hashtbl and inactive_list. Except
> > stripe_hashtbl and inactive_list, other fields are changed very rarely.
> >
> > With this patch, we split inactive_list and add new hash locks. Each free
> > stripe belongs to a specific inactive list. Which inactive list is determined
> > by stripe's lock_hash. Note, even a stripe hasn't a sector assigned, it has a
> > lock_hash assigned. Stripe's inactive list is protected by a hash lock, which
> > is determined by it's lock_hash too. The lock_hash is derivied from current
> > stripe_hashtbl hash, which guarantees any stripe_hashtbl list will be assigned
> > to a specific lock_hash, so we can use new hash lock to protect stripe_hashtbl
> > list too. The goal of the new hash locks introduced is we can only use the new
> > locks in the first path of get_active_stripe(). Since we have several hash
> > locks, lock contention is relieved significantly.
> >
> > The first path of get_active_stripe() accesses other fields, since they are
> > changed rarely, changing them now need take conf->device_lock and all hash
> > locks. For a slow path, this isn't a problem.
> >
> > If we need lock device_lock and hash lock, we always lock hash lock first. The
> > tricky part is release_stripe and friends. We need take device_lock first.
> > Neil's suggestion is we put inactive stripes to a temporary list and readd it
> > to inactive_list after device_lock is released. In this way, we add stripes to
> > temporary list with device_lock hold and remove stripes from the list with hash
> > lock hold. So we don't allow concurrent access to the temporary list, which
> > means we need allocate temporary list for all participants of release_stripe.
> >
> > One downside is free stripes are maintained in their inactive list, they can't
> > across between the lists. By default, we have total 256 stripes and 8 lists, so
> > each list will have 32 stripes. It's possible one list has free stripe but
> > other list hasn't. The chance should be rare because stripes allocation are
> > even distributed. And we can always allocate more stripes for cache, several
> > mega bytes memory isn't a big deal.
> >
> > This completely removes the lock contention of the first path of
> > get_active_stripe(). It slows down the second code path a little bit though
> > because we now need takes two locks, but since the hash lock isn't contended,
> > the overhead should be quite small (several atomic instructions). The second
> > path of get_active_stripe() (basically sequential write or big request size
> > randwrite) still has lock contentions.
> >
> > Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
> > ---
> > drivers/md/raid5.c | 346 ++++++++++++++++++++++++++++++++++++++++-------------
> > drivers/md/raid5.h | 11 +
> > 2 files changed, 276 insertions(+), 81 deletions(-)
> >
> > Index: linux/drivers/md/raid5.c
> > ===================================================================
> > --- linux.orig/drivers/md/raid5.c 2013-09-05 08:23:42.187851834 +0800
> > +++ linux/drivers/md/raid5.c 2013-09-05 12:52:47.581235145 +0800
> > @@ -86,6 +86,67 @@ static inline struct hlist_head *stripe_
> > return &conf->stripe_hashtbl[hash];
> > }
> >
> > +static inline int stripe_hash_locks_hash(sector_t sect)
> > +{
> > + return (sect >> STRIPE_SHIFT) & STRIPE_HASH_LOCKS_MASK;
> > +}
> > +
> > +static inline void lock_device_hash_lock(struct r5conf *conf, int hash)
> > +{
> > + spin_lock_irq(conf->hash_locks + hash);
> > + spin_lock(&conf->device_lock);
> > +}
> > +
> > +static inline void unlock_device_hash_lock(struct r5conf *conf, int hash)
> > +{
> > + spin_unlock(&conf->device_lock);
> > + spin_unlock_irq(conf->hash_locks + hash);
> > +}
> > +
> > +static void __lock_all_hash_locks(struct r5conf *conf)
> > +{
> > + int i;
> > + for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
> > + spin_lock(conf->hash_locks + i);
> > +}
> > +
> > +static void __unlock_all_hash_locks(struct r5conf *conf)
> > +{
> > + int i;
> > + for (i = NR_STRIPE_HASH_LOCKS; i; i--)
> > + spin_unlock(conf->hash_locks + i - 1);
> > +}
> > +
> > +static inline void lock_all_device_hash_locks_irq(struct r5conf *conf)
> > +{
> > + local_irq_disable();
> > + __lock_all_hash_locks(conf);
> > + spin_lock(&conf->device_lock);
> > +}
> > +
> > +static inline void unlock_all_device_hash_locks_irq(struct r5conf *conf)
> > +{
> > + spin_unlock(&conf->device_lock);
> > + __unlock_all_hash_locks(conf);
> > + local_irq_enable();
> > +}
> > +
> > +static inline void lock_all_device_hash_locks_irqsave(struct r5conf *conf,
> > + unsigned long *flags)
> > +{
> > + local_irq_save(*flags);
> > + __lock_all_hash_locks(conf);
> > + spin_lock(&conf->device_lock);
> > +}
> > +
> > +static inline void unlock_all_device_hash_locks_irqrestore(struct r5conf *conf,
> > + unsigned long *flags)
> > +{
> > + spin_unlock(&conf->device_lock);
> > + __unlock_all_hash_locks(conf);
> > + local_irq_restore(*flags);
> > +}
> > +
> > /* bio's attached to a stripe+device for I/O are linked together in bi_sector
> > * order without overlap. There may be several bio's per stripe+device, and
> > * a bio could span several devices.
> > @@ -250,7 +311,8 @@ static void raid5_wakeup_stripe_thread(s
> > }
> > }
> >
> > -static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh)
> > +static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh,
> > + struct list_head *temp_inactive_list)
> > {
> > BUG_ON(!list_empty(&sh->lru));
> > BUG_ON(atomic_read(&conf->active_stripes)==0);
> > @@ -279,19 +341,59 @@ static void do_release_stripe(struct r5c
> > < IO_THRESHOLD)
> > md_wakeup_thread(conf->mddev->thread);
> > atomic_dec(&conf->active_stripes);
> > - if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
> > - list_add_tail(&sh->lru, &conf->inactive_list);
> > - wake_up(&conf->wait_for_stripe);
> > - if (conf->retry_read_aligned)
> > - md_wakeup_thread(conf->mddev->thread);
> > - }
> > + if (!test_bit(STRIPE_EXPANDING, &sh->state))
> > + list_add_tail(&sh->lru, temp_inactive_list);
> > }
> > }
> >
> > -static void __release_stripe(struct r5conf *conf, struct stripe_head *sh)
> > +static void __release_stripe(struct r5conf *conf, struct stripe_head *sh,
> > + struct list_head *temp_inactive_list)
> > {
> > if (atomic_dec_and_test(&sh->count))
> > - do_release_stripe(conf, sh);
> > + do_release_stripe(conf, sh, temp_inactive_list);
> > +}
> > +
> > +/*
> > + * @hash could be NR_STRIPE_HASH_LOCKS, then we have a list of inactive_list
> > + *
> > + * Be careful: Only one task can add/delete stripes from temp_inactive_list at
> > + * given time. Adding stripes only takes device lock, while deleting stripes
> > + * only takes hash lock.
> > + */
> > +static void release_inactive_stripe_list(struct r5conf *conf,
> > + struct list_head *temp_inactive_list, int hash)
> > +{
> > + int size;
> > + bool do_wakeup = false;
> > + unsigned long flags;
> > +
> > + if (hash == NR_STRIPE_HASH_LOCKS) {
> > + size = NR_STRIPE_HASH_LOCKS;
> > + hash = NR_STRIPE_HASH_LOCKS - 1;
> > + } else
> > + size = 1;
> > + while (size) {
> > + struct list_head *list = &temp_inactive_list[size - 1];
> > +
> > + /*
> > + * We don't hold any lock here yet, get_active_stripe() might
> > + * remove stripes from the list
> > + */
> > + if (!list_empty_careful(list)) {
> > + spin_lock_irqsave(conf->hash_locks + hash, flags);
> > + list_splice_tail_init(list, conf->inactive_list + hash);
> > + do_wakeup = true;
> > + spin_unlock_irqrestore(conf->hash_locks + hash, flags);
> > + }
> > + size--;
> > + hash--;
> > + }
> > +
> > + if (do_wakeup) {
> > + wake_up(&conf->wait_for_stripe);
> > + if (conf->retry_read_aligned)
> > + md_wakeup_thread(conf->mddev->thread);
> > + }
> > }
> >
> > static struct llist_node *llist_reverse_order(struct llist_node *head)
> > @@ -309,7 +411,8 @@ static struct llist_node *llist_reverse_
> > }
> >
> > /* should hold conf->device_lock already */
> > -static int release_stripe_list(struct r5conf *conf)
> > +static int release_stripe_list(struct r5conf *conf,
> > + struct list_head *temp_inactive_list)
> > {
> > struct stripe_head *sh;
> > int count = 0;
> > @@ -318,6 +421,8 @@ static int release_stripe_list(struct r5
> > head = llist_del_all(&conf->released_stripes);
> > head = llist_reverse_order(head);
> > while (head) {
> > + int hash;
> > +
> > sh = llist_entry(head, struct stripe_head, release_list);
> > head = llist_next(head);
> > /* sh could be readded after STRIPE_ON_RELEASE_LIST is cleard */
> > @@ -328,7 +433,8 @@ static int release_stripe_list(struct r5
> > * again, the count is always > 1. This is true for
> > * STRIPE_ON_UNPLUG_LIST bit too.
> > */
> > - __release_stripe(conf, sh);
> > + hash = sh->hash_lock_index;
> > + __release_stripe(conf, sh, &temp_inactive_list[hash]);
> > count++;
> > }
> >
> > @@ -339,6 +445,8 @@ static void release_stripe(struct stripe
> > {
> > struct r5conf *conf = sh->raid_conf;
> > unsigned long flags;
> > + struct list_head list;
> > + int hash;
> > bool wakeup;
> >
> > if (test_and_set_bit(STRIPE_ON_RELEASE_LIST, &sh->state))
> > @@ -351,8 +459,11 @@ slow_path:
> > local_irq_save(flags);
> > /* we are ok here if STRIPE_ON_RELEASE_LIST is set or not */
> > if (atomic_dec_and_lock(&sh->count, &conf->device_lock)) {
> > - do_release_stripe(conf, sh);
> > + INIT_LIST_HEAD(&list);
> > + hash = sh->hash_lock_index;
> > + do_release_stripe(conf, sh, &list);
> > spin_unlock(&conf->device_lock);
> > + release_inactive_stripe_list(conf, &list, hash);
> > }
> > local_irq_restore(flags);
> > }
> > @@ -377,18 +488,19 @@ static inline void insert_hash(struct r5
> >
> >
> > /* find an idle stripe, make sure it is unhashed, and return it. */
> > -static struct stripe_head *get_free_stripe(struct r5conf *conf)
> > +static struct stripe_head *get_free_stripe(struct r5conf *conf, int hash)
> > {
> > struct stripe_head *sh = NULL;
> > struct list_head *first;
> >
> > - if (list_empty(&conf->inactive_list))
> > + if (list_empty(conf->inactive_list + hash))
> > goto out;
> > - first = conf->inactive_list.next;
> > + first = (conf->inactive_list + hash)->next;
> > sh = list_entry(first, struct stripe_head, lru);
> > list_del_init(first);
> > remove_hash(sh);
> > atomic_inc(&conf->active_stripes);
> > + BUG_ON(hash != sh->hash_lock_index);
> > out:
> > return sh;
> > }
> > @@ -567,33 +679,35 @@ get_active_stripe(struct r5conf *conf, s
> > int previous, int noblock, int noquiesce)
> > {
> > struct stripe_head *sh;
> > + int hash = stripe_hash_locks_hash(sector);
> >
> > pr_debug("get_stripe, sector %llu\n", (unsigned long long)sector);
> >
> > - spin_lock_irq(&conf->device_lock);
> > + spin_lock_irq(conf->hash_locks + hash);
> >
> > do {
> > wait_event_lock_irq(conf->wait_for_stripe,
> > conf->quiesce == 0 || noquiesce,
> > - conf->device_lock);
> > + *(conf->hash_locks + hash));
> > sh = __find_stripe(conf, sector, conf->generation - previous);
> > if (!sh) {
> > - if (!conf->inactive_blocked)
> > - sh = get_free_stripe(conf);
> > + sh = get_free_stripe(conf, hash);
> > if (noblock && sh == NULL)
> > break;
> > if (!sh) {
> > conf->inactive_blocked = 1;
> > wait_event_lock_irq(conf->wait_for_stripe,
> > - !list_empty(&conf->inactive_list) &&
> > - (atomic_read(&conf->active_stripes)
> > - < (conf->max_nr_stripes *3/4)
> > - || !conf->inactive_blocked),
> > - conf->device_lock);
> > + !list_empty(conf->inactive_list + hash) &&
> > + (atomic_read(&conf->active_stripes)
> > + < (conf->max_nr_stripes * 3 / 4)
> > + || !conf->inactive_blocked),
> > + *(conf->hash_locks + hash));
> > conf->inactive_blocked = 0;
> > } else
> > init_stripe(sh, sector, previous);
> > } else {
> > + spin_lock(&conf->device_lock);
> > +
> > if (atomic_read(&sh->count)) {
> > BUG_ON(!list_empty(&sh->lru)
> > && !test_bit(STRIPE_EXPANDING, &sh->state)
> > @@ -611,13 +725,14 @@ get_active_stripe(struct r5conf *conf, s
> > sh->group = NULL;
> > }
> > }
> > + spin_unlock(&conf->device_lock);
> > }
> > } while (sh == NULL);
> >
> > if (sh)
> > atomic_inc(&sh->count);
> >
> > - spin_unlock_irq(&conf->device_lock);
> > + spin_unlock_irq(conf->hash_locks + hash);
> > return sh;
> > }
> >
> > @@ -1585,7 +1700,7 @@ static void raid_run_ops(struct stripe_h
> > put_cpu();
> > }
> >
> > -static int grow_one_stripe(struct r5conf *conf)
> > +static int grow_one_stripe(struct r5conf *conf, int hash)
> > {
> > struct stripe_head *sh;
> > sh = kmem_cache_zalloc(conf->slab_cache, GFP_KERNEL);
> > @@ -1601,11 +1716,13 @@ static int grow_one_stripe(struct r5conf
> > kmem_cache_free(conf->slab_cache, sh);
> > return 0;
> > }
> > + sh->hash_lock_index = hash;
> > /* we just created an active stripe so... */
> > atomic_set(&sh->count, 1);
> > atomic_inc(&conf->active_stripes);
> > INIT_LIST_HEAD(&sh->lru);
> > release_stripe(sh);
> > + conf->max_hash_nr_stripes[hash]++;
> > return 1;
> > }
> >
> > @@ -1613,6 +1730,7 @@ static int grow_stripes(struct r5conf *c
> > {
> > struct kmem_cache *sc;
> > int devs = max(conf->raid_disks, conf->previous_raid_disks);
> > + int hash;
> >
> > if (conf->mddev->gendisk)
> > sprintf(conf->cache_name[0],
> > @@ -1630,9 +1748,12 @@ static int grow_stripes(struct r5conf *c
> > return 1;
> > conf->slab_cache = sc;
> > conf->pool_size = devs;
> > - while (num--)
> > - if (!grow_one_stripe(conf))
> > + hash = 0;
> > + while (num--) {
> > + if (!grow_one_stripe(conf, hash))
> > return 1;
> > + hash = (hash + 1) % NR_STRIPE_HASH_LOCKS;
> > + }
> > return 0;
> > }
> >
> > @@ -1690,6 +1811,7 @@ static int resize_stripes(struct r5conf
> > int err;
> > struct kmem_cache *sc;
> > int i;
> > + int hash, cnt;
> >
> > if (newsize <= conf->pool_size)
> > return 0; /* never bother to shrink */
> > @@ -1729,19 +1851,28 @@ static int resize_stripes(struct r5conf
> > * OK, we have enough stripes, start collecting inactive
> > * stripes and copying them over
> > */
> > + hash = 0;
> > + cnt = 0;
> > list_for_each_entry(nsh, &newstripes, lru) {
> > - spin_lock_irq(&conf->device_lock);
> > - wait_event_lock_irq(conf->wait_for_stripe,
> > - !list_empty(&conf->inactive_list),
> > - conf->device_lock);
> > - osh = get_free_stripe(conf);
> > - spin_unlock_irq(&conf->device_lock);
> > + lock_device_hash_lock(conf, hash);
> > + wait_event_cmd(conf->wait_for_stripe,
> > + !list_empty(conf->inactive_list + hash),
> > + unlock_device_hash_lock(conf, hash),
> > + lock_device_hash_lock(conf, hash));
> > + osh = get_free_stripe(conf, hash);
> > + unlock_device_hash_lock(conf, hash);
> > atomic_set(&nsh->count, 1);
> > for(i=0; i<conf->pool_size; i++)
> > nsh->dev[i].page = osh->dev[i].page;
> > for( ; i<newsize; i++)
> > nsh->dev[i].page = NULL;
> > + nsh->hash_lock_index = hash;
> > kmem_cache_free(conf->slab_cache, osh);
> > + cnt++;
> > + if (cnt >= conf->max_hash_nr_stripes[hash]) {
> > + hash++;
> > + cnt = 0;
> > + }
> > }
> > kmem_cache_destroy(conf->slab_cache);
> >
> > @@ -1800,13 +1931,14 @@ static int resize_stripes(struct r5conf
> > return err;
> > }
> >
> > -static int drop_one_stripe(struct r5conf *conf)
> > +static int drop_one_stripe(struct r5conf *conf, int hash)
> > {
> > struct stripe_head *sh;
> >
> > - spin_lock_irq(&conf->device_lock);
> > - sh = get_free_stripe(conf);
> > - spin_unlock_irq(&conf->device_lock);
> > + spin_lock_irq(conf->hash_locks + hash);
> > + sh = get_free_stripe(conf, hash);
> > + conf->max_hash_nr_stripes[hash]--;
> > + spin_unlock_irq(conf->hash_locks + hash);
> > if (!sh)
> > return 0;
> > BUG_ON(atomic_read(&sh->count));
> > @@ -1818,8 +1950,10 @@ static int drop_one_stripe(struct r5conf
> >
> > static void shrink_stripes(struct r5conf *conf)
> > {
> > - while (drop_one_stripe(conf))
> > - ;
> > + int hash;
> > + for (hash = 0; hash < NR_STRIPE_HASH_LOCKS; hash++)
> > + while (drop_one_stripe(conf, hash))
> > + ;
> >
> > if (conf->slab_cache)
> > kmem_cache_destroy(conf->slab_cache);
> > @@ -2048,10 +2182,10 @@ static void error(struct mddev *mddev, s
> > unsigned long flags;
> > pr_debug("raid456: error called\n");
> >
> > - spin_lock_irqsave(&conf->device_lock, flags);
> > + lock_all_device_hash_locks_irqsave(conf, &flags);
> > clear_bit(In_sync, &rdev->flags);
> > mddev->degraded = calc_degraded(conf);
> > - spin_unlock_irqrestore(&conf->device_lock, flags);
> > + unlock_all_device_hash_locks_irqrestore(conf, &flags);
> > set_bit(MD_RECOVERY_INTR, &mddev->recovery);
> >
> > set_bit(Blocked, &rdev->flags);
> > @@ -3895,7 +4029,8 @@ static void raid5_activate_delayed(struc
> > }
> > }
> >
> > -static void activate_bit_delay(struct r5conf *conf)
> > +static void activate_bit_delay(struct r5conf *conf,
> > + struct list_head *temp_inactive_list)
> > {
> > /* device_lock is held */
> > struct list_head head;
> > @@ -3903,9 +4038,11 @@ static void activate_bit_delay(struct r5
> > list_del_init(&conf->bitmap_list);
> > while (!list_empty(&head)) {
> > struct stripe_head *sh = list_entry(head.next, struct stripe_head, lru);
> > + int hash;
> > list_del_init(&sh->lru);
> > atomic_inc(&sh->count);
> > - __release_stripe(conf, sh);
> > + hash = sh->hash_lock_index;
> > + __release_stripe(conf, sh, &temp_inactive_list[hash]);
> > }
> > }
> >
> > @@ -3921,7 +4058,7 @@ int md_raid5_congested(struct mddev *mdd
> > return 1;
> > if (conf->quiesce)
> > return 1;
> > - if (list_empty_careful(&conf->inactive_list))
> > + if (atomic_read(&conf->active_stripes) == conf->max_nr_stripes)
> > return 1;
> >
> > return 0;
> > @@ -4251,6 +4388,7 @@ static struct stripe_head *__get_priorit
> > struct raid5_plug_cb {
> > struct blk_plug_cb cb;
> > struct list_head list;
> > + struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
> > };
> >
> > static void raid5_unplug(struct blk_plug_cb *blk_cb, bool from_schedule)
> > @@ -4261,6 +4399,7 @@ static void raid5_unplug(struct blk_plug
> > struct mddev *mddev = cb->cb.data;
> > struct r5conf *conf = mddev->private;
> > int cnt = 0;
> > + int hash;
> >
> > if (cb->list.next && !list_empty(&cb->list)) {
> > spin_lock_irq(&conf->device_lock);
> > @@ -4278,11 +4417,14 @@ static void raid5_unplug(struct blk_plug
> > * STRIPE_ON_RELEASE_LIST could be set here. In that
> > * case, the count is always > 1 here
> > */
> > - __release_stripe(conf, sh);
> > + hash = sh->hash_lock_index;
> > + __release_stripe(conf, sh, &cb->temp_inactive_list[hash]);
> > cnt++;
> > }
> > spin_unlock_irq(&conf->device_lock);
> > }
> > + release_inactive_stripe_list(conf, cb->temp_inactive_list,
> > + NR_STRIPE_HASH_LOCKS);
> > if (mddev->queue)
> > trace_block_unplug(mddev->queue, cnt, !from_schedule);
> > kfree(cb);
> > @@ -4303,8 +4445,12 @@ static void release_stripe_plug(struct m
> >
> > cb = container_of(blk_cb, struct raid5_plug_cb, cb);
> >
> > - if (cb->list.next == NULL)
> > + if (cb->list.next == NULL) {
> > + int i;
> > INIT_LIST_HEAD(&cb->list);
> > + for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
> > + INIT_LIST_HEAD(cb->temp_inactive_list + i);
> > + }
> >
> > if (!test_and_set_bit(STRIPE_ON_UNPLUG_LIST, &sh->state))
> > list_add_tail(&sh->lru, &cb->list);
> > @@ -4949,27 +5095,45 @@ static int retry_aligned_read(struct r5
> > }
> >
> > static int handle_active_stripes(struct r5conf *conf, int group,
> > - struct r5worker *worker)
> > + struct r5worker *worker,
> > + struct list_head *temp_inactive_list)
> > {
> > struct stripe_head *batch[MAX_STRIPE_BATCH], *sh;
> > - int i, batch_size = 0;
> > + int i, batch_size = 0, hash;
> > + bool release_inactive = false;
> >
> > while (batch_size < MAX_STRIPE_BATCH &&
> > (sh = __get_priority_stripe(conf, group)) != NULL)
> > batch[batch_size++] = sh;
> >
> > - if (batch_size == 0)
> > - return batch_size;
> > + if (batch_size == 0) {
> > + for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
> > + if (!list_empty(temp_inactive_list + i))
> > + break;
> > + if (i == NR_STRIPE_HASH_LOCKS)
> > + return batch_size;
> > + release_inactive = true;
> > + }
> > spin_unlock_irq(&conf->device_lock);
> >
> > + release_inactive_stripe_list(conf, temp_inactive_list,
> > + NR_STRIPE_HASH_LOCKS);
> > +
> > + if (release_inactive) {
> > + spin_lock_irq(&conf->device_lock);
> > + return 0;
> > + }
> > +
> > for (i = 0; i < batch_size; i++)
> > handle_stripe(batch[i]);
> >
> > cond_resched();
> >
> > spin_lock_irq(&conf->device_lock);
> > - for (i = 0; i < batch_size; i++)
> > - __release_stripe(conf, batch[i]);
> > + for (i = 0; i < batch_size; i++) {
> > + hash = batch[i]->hash_lock_index;
> > + __release_stripe(conf, batch[i], &temp_inactive_list[hash]);
> > + }
> > return batch_size;
> > }
> >
> > @@ -4990,9 +5154,10 @@ static void raid5_do_work(struct work_st
> > while (1) {
> > int batch_size, released;
> >
> > - released = release_stripe_list(conf);
> > + released = release_stripe_list(conf, worker->temp_inactive_list);
> >
> > - batch_size = handle_active_stripes(conf, group_id, worker);
> > + batch_size = handle_active_stripes(conf, group_id, worker,
> > + worker->temp_inactive_list);
> > worker->working = false;
> > if (!batch_size && !released)
> > break;
> > @@ -5031,7 +5196,7 @@ static void raid5d(struct md_thread *thr
> > struct bio *bio;
> > int batch_size, released;
> >
> > - released = release_stripe_list(conf);
> > + released = release_stripe_list(conf, conf->temp_inactive_list);
> >
> > if (
> > !list_empty(&conf->bitmap_list)) {
> > @@ -5041,7 +5206,7 @@ static void raid5d(struct md_thread *thr
> > bitmap_unplug(mddev->bitmap);
> > spin_lock_irq(&conf->device_lock);
> > conf->seq_write = conf->seq_flush;
> > - activate_bit_delay(conf);
> > + activate_bit_delay(conf, conf->temp_inactive_list);
> > }
> > raid5_activate_delayed(conf);
> >
> > @@ -5055,7 +5220,8 @@ static void raid5d(struct md_thread *thr
> > handled++;
> > }
> >
> > - batch_size = handle_active_stripes(conf, ANY_GROUP, NULL);
> > + batch_size = handle_active_stripes(conf, ANY_GROUP, NULL,
> > + conf->temp_inactive_list);
> > if (!batch_size && !released)
> > break;
> > handled += batch_size;
> > @@ -5091,22 +5257,28 @@ raid5_set_cache_size(struct mddev *mddev
> > {
> > struct r5conf *conf = mddev->private;
> > int err;
> > + int hash;
> >
> > if (size <= 16 || size > 32768)
> > return -EINVAL;
> > + size = round_up(size, NR_STRIPE_HASH_LOCKS);
> > + hash = 0;
> > while (size < conf->max_nr_stripes) {
> > - if (drop_one_stripe(conf))
> > + if (drop_one_stripe(conf, hash))
> > conf->max_nr_stripes--;
> > else
> > break;
> > + hash = (hash + 1) % NR_STRIPE_HASH_LOCKS;
> > }
> > err = md_allow_write(mddev);
> > if (err)
> > return err;
> > + hash = 0;
> > while (size > conf->max_nr_stripes) {
> > - if (grow_one_stripe(conf))
> > + if (grow_one_stripe(conf, hash))
> > conf->max_nr_stripes++;
> > else break;
> > + hash = (hash + 1) % NR_STRIPE_HASH_LOCKS;
> > }
> > return 0;
> > }
> > @@ -5257,7 +5429,7 @@ static struct attribute_group raid5_attr
> >
> > static int alloc_thread_groups(struct r5conf *conf, int cnt)
> > {
> > - int i, j;
> > + int i, j, k;
> > ssize_t size;
> > struct r5worker *workers;
> >
> > @@ -5287,8 +5459,12 @@ static int alloc_thread_groups(struct r5
> > group->workers = workers + i * cnt;
> >
> > for (j = 0; j < cnt; j++) {
> > - group->workers[j].group = group;
> > - INIT_WORK(&group->workers[j].work, raid5_do_work);
> > + struct r5worker *worker = group->workers + j;
> > + worker->group = group;
> > + INIT_WORK(&worker->work, raid5_do_work);
> > +
> > + for (k = 0; k < NR_STRIPE_HASH_LOCKS; k++)
> > + INIT_LIST_HEAD(worker->temp_inactive_list + k);
> > }
> > }
> >
> > @@ -5439,6 +5615,7 @@ static struct r5conf *setup_conf(struct
> > struct md_rdev *rdev;
> > struct disk_info *disk;
> > char pers_name[6];
> > + int i;
> >
> > if (mddev->new_level != 5
> > && mddev->new_level != 4
> > @@ -5483,7 +5660,6 @@ static struct r5conf *setup_conf(struct
> > INIT_LIST_HEAD(&conf->hold_list);
> > INIT_LIST_HEAD(&conf->delayed_list);
> > INIT_LIST_HEAD(&conf->bitmap_list);
> > - INIT_LIST_HEAD(&conf->inactive_list);
> > init_llist_head(&conf->released_stripes);
> > atomic_set(&conf->active_stripes, 0);
> > atomic_set(&conf->preread_active_stripes, 0);
> > @@ -5509,6 +5685,15 @@ static struct r5conf *setup_conf(struct
> > if ((conf->stripe_hashtbl = kzalloc(PAGE_SIZE, GFP_KERNEL)) == NULL)
> > goto abort;
> >
> > + for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
> > + spin_lock_init(conf->hash_locks + i);
> > +
> > + for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
> > + INIT_LIST_HEAD(conf->inactive_list + i);
> > +
> > + for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
> > + INIT_LIST_HEAD(conf->temp_inactive_list + i);
> > +
> > conf->level = mddev->new_level;
> > if (raid5_alloc_percpu(conf) != 0)
> > goto abort;
> > @@ -6034,9 +6219,9 @@ static int raid5_spare_active(struct mdd
> > sysfs_notify_dirent_safe(tmp->rdev->sysfs_state);
> > }
> > }
> > - spin_lock_irqsave(&conf->device_lock, flags);
> > + lock_all_device_hash_locks_irqsave(conf, &flags);
> > mddev->degraded = calc_degraded(conf);
> > - spin_unlock_irqrestore(&conf->device_lock, flags);
> > + unlock_all_device_hash_locks_irqrestore(conf, &flags);
> > print_raid5_conf(conf);
> > return count;
> > }
> > @@ -6347,9 +6532,9 @@ static int raid5_start_reshape(struct md
> > * ->degraded is measured against the larger of the
> > * pre and post number of devices.
> > */
> > - spin_lock_irqsave(&conf->device_lock, flags);
> > + lock_all_device_hash_locks_irqsave(conf, &flags);
> > mddev->degraded = calc_degraded(conf);
> > - spin_unlock_irqrestore(&conf->device_lock, flags);
> > + unlock_all_device_hash_locks_irqrestore(conf, &flags);
> > }
> > mddev->raid_disks = conf->raid_disks;
> > mddev->reshape_position = conf->reshape_progress;
> > @@ -6363,14 +6548,14 @@ static int raid5_start_reshape(struct md
> > "reshape");
> > if (!mddev->sync_thread) {
> > mddev->recovery = 0;
> > - spin_lock_irq(&conf->device_lock);
> > + lock_all_device_hash_locks_irq(conf);
> > mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
> > rdev_for_each(rdev, mddev)
> > rdev->new_data_offset = rdev->data_offset;
> > smp_wmb();
> > conf->reshape_progress = MaxSector;
> > mddev->reshape_position = MaxSector;
> > - spin_unlock_irq(&conf->device_lock);
> > + unlock_all_device_hash_locks_irq(conf);
> > return -EAGAIN;
> > }
> > conf->reshape_checkpoint = jiffies;
> > @@ -6388,13 +6573,13 @@ static void end_reshape(struct r5conf *c
> > if (!test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery)) {
> > struct md_rdev *rdev;
> >
> > - spin_lock_irq(&conf->device_lock);
> > + lock_all_device_hash_locks_irq(conf);
> > conf->previous_raid_disks = conf->raid_disks;
> > rdev_for_each(rdev, conf->mddev)
> > rdev->data_offset = rdev->new_data_offset;
> > smp_wmb();
> > conf->reshape_progress = MaxSector;
> > - spin_unlock_irq(&conf->device_lock);
> > + unlock_all_device_hash_locks_irq(conf);
> > wake_up(&conf->wait_for_overlap);
> >
> > /* read-ahead size must cover two whole stripes, which is
> > @@ -6425,9 +6610,9 @@ static void raid5_finish_reshape(struct
> > revalidate_disk(mddev->gendisk);
> > } else {
> > int d;
> > - spin_lock_irq(&conf->device_lock);
> > + lock_all_device_hash_locks_irq(conf);
> > mddev->degraded = calc_degraded(conf);
> > - spin_unlock_irq(&conf->device_lock);
> > + unlock_all_device_hash_locks_irq(conf);
> > for (d = conf->raid_disks ;
> > d < conf->raid_disks - mddev->delta_disks;
> > d++) {
> > @@ -6457,27 +6642,28 @@ static void raid5_quiesce(struct mddev *
> > break;
> >
> > case 1: /* stop all writes */
> > - spin_lock_irq(&conf->device_lock);
> > + lock_all_device_hash_locks_irq(conf);
> > /* '2' tells resync/reshape to pause so that all
> > * active stripes can drain
> > */
> > conf->quiesce = 2;
> > - wait_event_lock_irq(conf->wait_for_stripe,
> > + wait_event_cmd(conf->wait_for_stripe,
> > atomic_read(&conf->active_stripes) == 0 &&
> > atomic_read(&conf->active_aligned_reads) == 0,
> > - conf->device_lock);
> > + unlock_all_device_hash_locks_irq(conf),
> > + lock_all_device_hash_locks_irq(conf));
> > conf->quiesce = 1;
> > - spin_unlock_irq(&conf->device_lock);
> > + unlock_all_device_hash_locks_irq(conf);
> > /* allow reshape to continue */
> > wake_up(&conf->wait_for_overlap);
> > break;
> >
> > case 0: /* re-enable writes */
> > - spin_lock_irq(&conf->device_lock);
> > + lock_all_device_hash_locks_irq(conf);
> > conf->quiesce = 0;
> > wake_up(&conf->wait_for_stripe);
> > wake_up(&conf->wait_for_overlap);
> > - spin_unlock_irq(&conf->device_lock);
> > + unlock_all_device_hash_locks_irq(conf);
> > break;
> > }
> > }
> > Index: linux/drivers/md/raid5.h
> > ===================================================================
> > --- linux.orig/drivers/md/raid5.h 2013-09-05 08:23:42.187851834 +0800
> > +++ linux/drivers/md/raid5.h 2013-09-05 08:30:49.090484930 +0800
> > @@ -205,6 +205,7 @@ struct stripe_head {
> > short pd_idx; /* parity disk index */
> > short qd_idx; /* 'Q' disk index for raid6 */
> > short ddf_layout;/* use DDF ordering to calculate Q */
> > + short hash_lock_index;
> > unsigned long state; /* state flags */
> > atomic_t count; /* nr of active thread/requests */
> > int bm_seq; /* sequence number for bitmap flushes */
> > @@ -367,9 +368,13 @@ struct disk_info {
> > struct md_rdev *rdev, *replacement;
> > };
> >
> > +#define NR_STRIPE_HASH_LOCKS 8
> > +#define STRIPE_HASH_LOCKS_MASK (NR_STRIPE_HASH_LOCKS - 1)
> > +
> > struct r5worker {
> > struct work_struct work;
> > struct r5worker_group *group;
> > + struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
> > bool working;
> > };
> >
> > @@ -382,6 +387,8 @@ struct r5worker_group {
> >
> > struct r5conf {
> > struct hlist_head *stripe_hashtbl;
> > + /* only protect corresponding hash list and inactive_list */
> > + spinlock_t hash_locks[NR_STRIPE_HASH_LOCKS];
> > struct mddev *mddev;
> > int chunk_sectors;
> > int level, algorithm;
> > @@ -462,7 +469,8 @@ struct r5conf {
> > * Free stripes pool
> > */
> > atomic_t active_stripes;
> > - struct list_head inactive_list;
> > + struct list_head inactive_list[NR_STRIPE_HASH_LOCKS];
> > + int max_hash_nr_stripes[NR_STRIPE_HASH_LOCKS];
> > struct llist_head released_stripes;
> > wait_queue_head_t wait_for_stripe;
> > wait_queue_head_t wait_for_overlap;
> > @@ -477,6 +485,7 @@ struct r5conf {
> > * the new thread here until we fully activate the array.
> > */
> > struct md_thread *thread;
> > + struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
> > struct r5worker_group *worker_groups;
> > int group_cnt;
> > int worker_cnt_per_group;
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>
> Hi,
> thanks for this. It is looking quite good.
>
> I don't really like max_hash_nr_stripes though.
> I note that you round up the cache_size to a multiple of
> NR_STRIPE_HASH_LOCKS.
> I think that is a good idea and should allow us to ensure that every hash
> value always has the same number of stripe_heads.
> If we get a failure when allocating, we would need to free some to bring it
> back to a uniform number.
ok, I can do this.
> I'm in two minds about the temp_inactive_list.
> An alternative would be to have a single list and use list_sort() to sort it
> by hash_lock_index before moving the stripe_heads to the relevant lists,
> taking one lock at a time.
> This save some memory and costs some cpu time. On the whole I think it
> gains in elegance but I'm not sure. What do you think?
I thought it doesn't work. For example, we lock hash 0 lock.
get_active_stripe() finds a stripe of hash 1, and delete it from lru, while the
stripe is in temp_inactive_list. We are locking different hash locks, so the
list could corrupt. Alternative is we hold device_lock again and move one
hash's temp_active_list to another list, then unlock device_lock. then do
releae for the new temporary list. But in this way, we need take device_lock
several times, which isn't good too.
Thanks,
Shaohua
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