[PATCH rdma-next v1 2/5] RDMA/mlx5: Replace cache list with Xarray

From: Michael Guralnik
Date: Tue Jul 26 2022 - 03:20:02 EST

From: Aharon Landau <aharonl@xxxxxxxxxx>

The Xarray allows us to store the cached mkeys in memory efficient way.

Entries are reserved in the Xarray using xa_cmpxchg before calling to
the upcoming callbacks to avoid allocations in interrupt context.
The xa_cmpxchg can sleep when using GFP_KERNEL, so we call it in
a loop to ensure one reserved entry for each process trying to reserve.

Signed-off-by: Aharon Landau <aharonl@xxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
---
drivers/infiniband/hw/mlx5/mlx5_ib.h | 14 +-
drivers/infiniband/hw/mlx5/mr.c | 226 ++++++++++++++++++---------
2 files changed, 152 insertions(+), 88 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
index 42bc58967b1f..e0eb666aefa1 100644
--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -651,8 +651,6 @@ struct mlx5_ib_mr {
struct {
u32 out[MLX5_ST_SZ_DW(create_mkey_out)];
struct mlx5_async_work cb_work;
- /* Cache list element */
- struct list_head list;
};

/* Used only by kernel MRs (umem == NULL) */
@@ -744,7 +742,8 @@ struct umr_common {

struct mlx5_cache_ent {
struct xarray mkeys;
- struct list_head head;
+ unsigned long stored;
+ unsigned long reserved;

char name[4];
u32 order;
@@ -756,18 +755,13 @@ struct mlx5_cache_ent {
u8 fill_to_high_water:1;

/*
- * - available_mrs is the length of list head, ie the number of MRs
- * available for immediate allocation.
- * - total_mrs is available_mrs plus all in use MRs that could be
+ * - total_mrs is stored mkeys plus all in use MRs that could be
* returned to the cache.
- * - limit is the low water mark for available_mrs, 2* limit is the
+ * - limit is the low water mark for stored mkeys, 2* limit is the
* upper water mark.
- * - pending is the number of MRs currently being created
*/
u32 total_mrs;
- u32 available_mrs;
u32 limit;
- u32 pending;

/* Statistics */
u32 miss;
diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
index d56e7ff74b98..cbb8882c7787 100644
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -142,6 +142,104 @@ static void create_mkey_warn(struct mlx5_ib_dev *dev, int status, void *out)
mlx5_cmd_out_err(dev->mdev, MLX5_CMD_OP_CREATE_MKEY, 0, out);
}

+
+static int push_mkey(struct mlx5_cache_ent *ent, bool limit_pendings,
+ void *to_store)
+{
+ XA_STATE(xas, &ent->mkeys, 0);
+ void *curr;
+
+ xa_lock_irq(&ent->mkeys);
+ if (limit_pendings &&
+ (ent->reserved - ent->stored) > MAX_PENDING_REG_MR) {
+ xa_unlock_irq(&ent->mkeys);
+ return -EAGAIN;
+ }
+ while (1) {
+ /*
+ * This is cmpxchg (NULL, XA_ZERO_ENTRY) however this version
+ * doesn't transparently unlock. Instead we set the xas index to
+ * the current value of reserved every iteration.
+ */
+ xas_set(&xas, ent->reserved);
+ curr = xas_load(&xas);
+ if (!curr) {
+ if (to_store && ent->stored == ent->reserved)
+ xas_store(&xas, to_store);
+ else
+ xas_store(&xas, XA_ZERO_ENTRY);
+ if (xas_valid(&xas)) {
+ ent->reserved++;
+ if (to_store) {
+ if (ent->stored != ent->reserved)
+ __xa_store(&ent->mkeys,
+ ent->stored,
+ to_store,
+ GFP_KERNEL);
+ ent->stored++;
+ queue_adjust_cache_locked(ent);
+ WRITE_ONCE(ent->dev->cache.last_add,
+ jiffies);
+ }
+ }
+ }
+ xa_unlock_irq(&ent->mkeys);
+
+ /*
+ * Notice xas_nomem() must always be called as it cleans
+ * up any cached allocation.
+ */
+ if (!xas_nomem(&xas, GFP_KERNEL))
+ break;
+ xa_lock_irq(&ent->mkeys);
+ }
+ if (xas_error(&xas))
+ return xas_error(&xas);
+ if (WARN_ON(curr))
+ return -EINVAL;
+ return 0;
+}
+
+static void undo_push_reserve_mkey(struct mlx5_cache_ent *ent)
+{
+ void *old;
+
+ ent->reserved--;
+ old = __xa_erase(&ent->mkeys, ent->reserved);
+ WARN_ON(old);
+}
+
+static void push_to_reserved(struct mlx5_cache_ent *ent, struct mlx5_ib_mr *mr)
+{
+ void *old;
+
+ old = __xa_store(&ent->mkeys, ent->stored, mr, 0);
+ WARN_ON(old);
+ ent->stored++;
+}
+
+static struct mlx5_ib_mr *pop_stored_mkey(struct mlx5_cache_ent *ent)
+{
+ struct mlx5_ib_mr *mr;
+ void *old;
+
+ ent->stored--;
+ ent->reserved--;
+
+ if (ent->stored == ent->reserved) {
+ mr = __xa_erase(&ent->mkeys, ent->stored);
+ WARN_ON(!mr);
+ return mr;
+ }
+
+ mr = __xa_store(&ent->mkeys, ent->stored, XA_ZERO_ENTRY,
+ GFP_KERNEL);
+ WARN_ON(!mr || xa_is_err(mr));
+ old = __xa_erase(&ent->mkeys, ent->reserved);
+ WARN_ON(old);
+ return mr;
+}
+
static void create_mkey_callback(int status, struct mlx5_async_work *context)
{
struct mlx5_ib_mr *mr =
@@ -154,7 +252,7 @@ static void create_mkey_callback(int status, struct mlx5_async_work *context)
create_mkey_warn(dev, status, mr->out);
kfree(mr);
xa_lock_irqsave(&ent->mkeys, flags);
- ent->pending--;
+ undo_push_reserve_mkey(ent);
WRITE_ONCE(dev->fill_delay, 1);
xa_unlock_irqrestore(&ent->mkeys, flags);
mod_timer(&dev->delay_timer, jiffies + HZ);
@@ -169,12 +267,10 @@ static void create_mkey_callback(int status, struct mlx5_async_work *context)
WRITE_ONCE(dev->cache.last_add, jiffies);

xa_lock_irqsave(&ent->mkeys, flags);
- list_add_tail(&mr->list, &ent->head);
- ent->available_mrs++;
+ push_to_reserved(ent, mr);
ent->total_mrs++;
/* If we are doing fill_to_high_water then keep going. */
queue_adjust_cache_locked(ent);
- ent->pending--;
xa_unlock_irqrestore(&ent->mkeys, flags);
}

@@ -237,31 +333,33 @@ static int add_keys(struct mlx5_cache_ent *ent, unsigned int num)
mr = alloc_cache_mr(ent, mkc);
if (!mr) {
err = -ENOMEM;
- break;
+ goto free_in;
}
- xa_lock_irq(&ent->mkeys);
- if (ent->pending >= MAX_PENDING_REG_MR) {
- err = -EAGAIN;
- xa_unlock_irq(&ent->mkeys);
- kfree(mr);
- break;
- }
- ent->pending++;
- xa_unlock_irq(&ent->mkeys);
+
+ err = push_mkey(ent, true, NULL);
+ if (err)
+ goto free_mr;
+
err = mlx5_ib_create_mkey_cb(ent->dev, &mr->mmkey,
&ent->dev->async_ctx, in, inlen,
mr->out, sizeof(mr->out),
&mr->cb_work);
if (err) {
- xa_lock_irq(&ent->mkeys);
- ent->pending--;
- xa_unlock_irq(&ent->mkeys);
mlx5_ib_warn(ent->dev, "create mkey failed %d\n", err);
- kfree(mr);
- break;
+ goto err_undo_reserve;
}
}

+ kfree(in);
+ return 0;
+
+err_undo_reserve:
+ xa_lock_irq(&ent->mkeys);
+ undo_push_reserve_mkey(ent);
+ xa_unlock_irq(&ent->mkeys);
+free_mr:
+ kfree(mr);
+free_in:
kfree(in);
return err;
}
@@ -310,11 +408,9 @@ static void remove_cache_mr_locked(struct mlx5_cache_ent *ent)
struct mlx5_ib_mr *mr;

lockdep_assert_held(&ent->mkeys.xa_lock);
- if (list_empty(&ent->head))
+ if (!ent->stored)
return;
- mr = list_first_entry(&ent->head, struct mlx5_ib_mr, list);
- list_del(&mr->list);
- ent->available_mrs--;
+ mr = pop_stored_mkey(ent);
ent->total_mrs--;
xa_unlock_irq(&ent->mkeys);
mlx5_core_destroy_mkey(ent->dev->mdev, mr->mmkey.key);
@@ -324,6 +420,7 @@ static void remove_cache_mr_locked(struct mlx5_cache_ent *ent)

static int resize_available_mrs(struct mlx5_cache_ent *ent, unsigned int target,
bool limit_fill)
+ __acquires(&ent->mkeys) __releases(&ent->mkeys)
{
int err;

@@ -332,10 +429,10 @@ static int resize_available_mrs(struct mlx5_cache_ent *ent, unsigned int target,
while (true) {
if (limit_fill)
target = ent->limit * 2;
- if (target == ent->available_mrs + ent->pending)
+ if (target == ent->reserved)
return 0;
- if (target > ent->available_mrs + ent->pending) {
- u32 todo = target - (ent->available_mrs + ent->pending);
+ if (target > ent->reserved) {
+ u32 todo = target - ent->reserved;

xa_unlock_irq(&ent->mkeys);
err = add_keys(ent, todo);
@@ -366,15 +463,15 @@ static ssize_t size_write(struct file *filp, const char __user *buf,

/*
* Target is the new value of total_mrs the user requests, however we
- * cannot free MRs that are in use. Compute the target value for
- * available_mrs.
+ * cannot free MRs that are in use. Compute the target value for stored
+ * mkeys.
*/
xa_lock_irq(&ent->mkeys);
- if (target < ent->total_mrs - ent->available_mrs) {
+ if (target < ent->total_mrs - ent->stored) {
err = -EINVAL;
goto err_unlock;
}
- target = target - (ent->total_mrs - ent->available_mrs);
+ target = target - (ent->total_mrs - ent->stored);
if (target < ent->limit || target > ent->limit*2) {
err = -EINVAL;
goto err_unlock;
@@ -466,7 +563,7 @@ static bool someone_adding(struct mlx5_mr_cache *cache)
bool ret;

xa_lock_irq(&ent->mkeys);
- ret = ent->available_mrs < ent->limit;
+ ret = ent->stored < ent->limit;
xa_unlock_irq(&ent->mkeys);
if (ret)
return true;
@@ -485,22 +582,22 @@ static void queue_adjust_cache_locked(struct mlx5_cache_ent *ent)

if (ent->disabled || READ_ONCE(ent->dev->fill_delay))
return;
- if (ent->available_mrs < ent->limit) {
+ if (ent->stored < ent->limit) {
ent->fill_to_high_water = true;
mod_delayed_work(ent->dev->cache.wq, &ent->dwork, 0);
} else if (ent->fill_to_high_water &&
- ent->available_mrs + ent->pending < 2 * ent->limit) {
+ ent->reserved < 2 * ent->limit) {
/*
* Once we start populating due to hitting a low water mark
* continue until we pass the high water mark.
*/
mod_delayed_work(ent->dev->cache.wq, &ent->dwork, 0);
- } else if (ent->available_mrs == 2 * ent->limit) {
+ } else if (ent->stored == 2 * ent->limit) {
ent->fill_to_high_water = false;
- } else if (ent->available_mrs > 2 * ent->limit) {
+ } else if (ent->stored > 2 * ent->limit) {
/* Queue deletion of excess entries */
ent->fill_to_high_water = false;
- if (ent->pending)
+ if (ent->stored != ent->reserved)
queue_delayed_work(ent->dev->cache.wq, &ent->dwork,
msecs_to_jiffies(1000));
else
@@ -518,8 +615,7 @@ static void __cache_work_func(struct mlx5_cache_ent *ent)
if (ent->disabled)
goto out;

- if (ent->fill_to_high_water &&
- ent->available_mrs + ent->pending < 2 * ent->limit &&
+ if (ent->fill_to_high_water && ent->reserved < 2 * ent->limit &&
!READ_ONCE(dev->fill_delay)) {
xa_unlock_irq(&ent->mkeys);
err = add_keys(ent, 1);
@@ -528,8 +624,8 @@ static void __cache_work_func(struct mlx5_cache_ent *ent)
goto out;
if (err) {
/*
- * EAGAIN only happens if pending is positive, so we
- * will be rescheduled from reg_mr_callback(). The only
+ * EAGAIN only happens if there are pending MRs, so we
+ * will be rescheduled when storing them. The only
* failure path here is ENOMEM.
*/
if (err != -EAGAIN) {
@@ -541,7 +637,7 @@ static void __cache_work_func(struct mlx5_cache_ent *ent)
msecs_to_jiffies(1000));
}
}
- } else if (ent->available_mrs > 2 * ent->limit) {
+ } else if (ent->stored > 2 * ent->limit) {
bool need_delay;

/*
@@ -593,7 +689,7 @@ struct mlx5_ib_mr *mlx5_mr_cache_alloc(struct mlx5_ib_dev *dev,
return ERR_PTR(-EOPNOTSUPP);

xa_lock_irq(&ent->mkeys);
- if (list_empty(&ent->head)) {
+ if (!ent->stored) {
queue_adjust_cache_locked(ent);
ent->miss++;
xa_unlock_irq(&ent->mkeys);
@@ -601,9 +697,7 @@ struct mlx5_ib_mr *mlx5_mr_cache_alloc(struct mlx5_ib_dev *dev,
if (IS_ERR(mr))
return mr;
} else {
- mr = list_first_entry(&ent->head, struct mlx5_ib_mr, list);
- list_del(&mr->list);
- ent->available_mrs--;
+ mr = pop_stored_mkey(ent);
queue_adjust_cache_locked(ent);
xa_unlock_irq(&ent->mkeys);

@@ -612,45 +706,23 @@ struct mlx5_ib_mr *mlx5_mr_cache_alloc(struct mlx5_ib_dev *dev,
return mr;
}

-static void mlx5_mr_cache_free(struct mlx5_ib_dev *dev, struct mlx5_ib_mr *mr)
-{
- struct mlx5_cache_ent *ent = mr->cache_ent;
-
- WRITE_ONCE(dev->cache.last_add, jiffies);
- xa_lock_irq(&ent->mkeys);
- list_add_tail(&mr->list, &ent->head);
- ent->available_mrs++;
- queue_adjust_cache_locked(ent);
- xa_unlock_irq(&ent->mkeys);
-}
-
static void clean_keys(struct mlx5_ib_dev *dev, int c)
{
struct mlx5_mr_cache *cache = &dev->cache;
struct mlx5_cache_ent *ent = &cache->ent[c];
- struct mlx5_ib_mr *tmp_mr;
struct mlx5_ib_mr *mr;
- LIST_HEAD(del_list);

cancel_delayed_work(&ent->dwork);
- while (1) {
- xa_lock_irq(&ent->mkeys);
- if (list_empty(&ent->head)) {
- xa_unlock_irq(&ent->mkeys);
- break;
- }
- mr = list_first_entry(&ent->head, struct mlx5_ib_mr, list);
- list_move(&mr->list, &del_list);
- ent->available_mrs--;
+ xa_lock_irq(&ent->mkeys);
+ while (ent->stored) {
+ mr = pop_stored_mkey(ent);
ent->total_mrs--;
xa_unlock_irq(&ent->mkeys);
mlx5_core_destroy_mkey(dev->mdev, mr->mmkey.key);
- }
-
- list_for_each_entry_safe(mr, tmp_mr, &del_list, list) {
- list_del(&mr->list);
kfree(mr);
+ xa_lock_irq(&ent->mkeys);
}
+ xa_unlock_irq(&ent->mkeys);
}

static void mlx5_mr_cache_debugfs_cleanup(struct mlx5_ib_dev *dev)
@@ -680,7 +752,7 @@ static void mlx5_mr_cache_debugfs_init(struct mlx5_ib_dev *dev)
dir = debugfs_create_dir(ent->name, cache->root);
debugfs_create_file("size", 0600, dir, ent, &size_fops);
debugfs_create_file("limit", 0600, dir, ent, &limit_fops);
- debugfs_create_u32("cur", 0400, dir, &ent->available_mrs);
+ debugfs_create_ulong("cur", 0400, dir, &ent->stored);
debugfs_create_u32("miss", 0600, dir, &ent->miss);
}
}
@@ -709,7 +781,6 @@ int mlx5_mr_cache_init(struct mlx5_ib_dev *dev)
timer_setup(&dev->delay_timer, delay_time_func, 0);
for (i = 0; i < MAX_MR_CACHE_ENTRIES; i++) {
ent = &cache->ent[i];
- INIT_LIST_HEAD(&ent->head);
xa_init_flags(&ent->mkeys, XA_FLAGS_LOCK_IRQ);
ent->order = i + 2;
ent->dev = dev;
@@ -1571,7 +1642,8 @@ int mlx5_ib_dereg_mr(struct ib_mr *ibmr, struct ib_udata *udata)

/* Stop DMA */
if (mr->cache_ent) {
- if (mlx5r_umr_revoke_mr(mr)) {
+ if (mlx5r_umr_revoke_mr(mr) ||
+ push_mkey(mr->cache_ent, false, mr)) {
xa_lock_irq(&mr->cache_ent->mkeys);
mr->cache_ent->total_mrs--;
xa_unlock_irq(&mr->cache_ent->mkeys);
@@ -1595,9 +1667,7 @@ int mlx5_ib_dereg_mr(struct ib_mr *ibmr, struct ib_udata *udata)
mlx5_ib_free_odp_mr(mr);
}

- if (mr->cache_ent) {
- mlx5_mr_cache_free(dev, mr);
- } else {
+ if (!mr->cache_ent) {
mlx5_free_priv_descs(mr);
kfree(mr);
}
--
2.17.2