[PATCH rdma-next v2 0/3] cgroup/rdma: add MR memory size resource tracking

[PATCH rdma-next v2 0/3] cgroup/rdma: add MR memory size resource tracking

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

Currently the RDMA cgroup only tracks two aggregate counters:
hca_handle and hca_object.  The real scarce resource in multi-tenant
deployments is pinned memory: how much physical memory gets registered
through MRs.  The existing hca_object counter is too coarse to capture
this.

This series adds a single new resource type:

  - mr_mem  - Cumulative MR memory size in bytes

The per-object-type counters (qp, mr) from RFC v1 have been removed
per review feedback [1]: modern NICs pool objects from the same memory
pool so the distinction between QP count and MR count is not
meaningful for resource limiting.  hca_object remains sufficient for
coarse object accounting.

After this series, an administrator can set limits like:

    echo "mlx5_0 mr_mem=1073741824" > rdma.max

Design
~~~~~~

mr_mem is not page-level ownership tracking; it is object-based
accounting tied to the MR lifetime:

  - charged at MR registration time
  - uncharged at MR destruction time
  - the charge is pinned to the cgroup that created the MR for the
    entire lifetime of the MR object

This model intentionally defines accounting semantics around MR
object lifetime rather than page ownership:

1. fork(): fork() does not duplicate MR objects.  Even though the
   child inherits the uverbs fd and can access the parent's ucontext,
   the MR remains a single kernel object.  The charge is tied to the
   MR object, not to the number of processes that can reach it, so
   no splitting or re-accounting is needed.

2. Cgroup migration: mr_mem follows the same semantics as the existing
   hca_object; charge at creation time against the invoking task's
   cgroup, uncharge at destruction time.  The RDMA cgroup does not
   implement can_attach/attach callbacks today, so charges do not
   migrate with the task.  This is a known limitation that applies
   equally to hca_handle and hca_object.  mr_mem does not introduce
   any new complication here.

3. Overlap with memory cgroup: mr_mem does not count process memory
   usage; it represents a per-device DMA registration budget: the
   amount of memory this cgroup may register through a given HCA.
   This is a different dimension from what memory cgroup tracks.  An
   administrator might set mr_mem limits differently per device, which
   memory cgroup cannot express.

   In particular, mr_mem tracks the registered memory range associated
   with the MR rather than exact dynamically pinned pages (e.g. for
   ODP MRs).  This is a stable, policy-oriented approximation of
   registration footprint, not an attempt at precise physical page
   accounting.

Tao Cui (3):
  cgroup/rdma: extend charge/uncharge API with s64 amount parameter
  cgroup/rdma: add MR memory size resource tracking
  cgroup/rdma: update cgroup resource list for MR_MEM

 Documentation/admin-guide/cgroup-v2.rst       |  21 ++--
 drivers/infiniband/core/cgroup.c              |  10 +-
 drivers/infiniband/core/core_priv.h           |  12 +-
 drivers/infiniband/core/rdma_core.c           |  20 +++-
 drivers/infiniband/core/uverbs_cmd.c          |  61 +++++++++-
 drivers/infiniband/core/uverbs_std_types_mr.c |  37 ++++++
 include/linux/cgroup_rdma.h                   |   8 +-
 include/rdma/ib_verbs.h                       |   1 +
 kernel/cgroup/rdma.c                          | 108 +++++++++++++-----
 9 files changed, 219 insertions(+), 59 deletions(-)

---
Changes from RFC v1:

  - Removed RDMACG_RESOURCE_QP and RDMACG_RESOURCE_MR per-type
    counters following review feedback from Jason Gunthorpe [1].
  - Retained only RDMACG_RESOURCE_MR_MEM as the sole new resource.
  - Added detailed semantic notes to the commit messages addressing
    fork(), cgroup migration, and overlap with memory cgroup [2].
  - Renamed patches to reflect the narrower scope.

[1] https://lore.kernel.org/all/20260525134314.GI7702@ziepe.ca/
[2] https://lore.kernel.org/all/20260528075537.2170697-1-cuitao@kylinos.cn/
-- 
2.43.0

[PATCH rdma-next v2 1/3] cgroup/rdma: extend charge/uncharge API with s64 amount parameter

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

Change struct rdmacg_resource fields (max, usage, peak) and all
charge/uncharge function signatures from int to s64 to prepare for
byte-sized resource tracking such as MR memory.

Replace match_int with a match_s64 helper that uses kstrtoll so the
user-space limit tokens accept 64-bit values.  All existing callers
pass amount=1 (count-based), so the change is transparent for
existing count-based resources.

The rpool->usage_sum counter continues to track the number of active
charge operations (not the sum of charged amounts); this is correct
because it governs rpool lifetime - a pool is releasable only when
all charges, regardless of amount, have been released.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 drivers/infiniband/core/cgroup.c     | 10 ++--
 drivers/infiniband/core/core_priv.h  | 12 ++--
 drivers/infiniband/core/rdma_core.c  |  8 +--
 drivers/infiniband/core/uverbs_cmd.c |  4 +-
 include/linux/cgroup_rdma.h          |  7 ++-
 kernel/cgroup/rdma.c                 | 87 ++++++++++++++++++----------
 6 files changed, 83 insertions(+), 45 deletions(-)

diff --git a/drivers/infiniband/core/cgroup.c b/drivers/infiniband/core/cgroup.c
index 1f037fe01450..81e24de72392 100644
--- a/drivers/infiniband/core/cgroup.c
+++ b/drivers/infiniband/core/cgroup.c
@@ -36,18 +36,20 @@ void ib_device_unregister_rdmacg(struct ib_device *device)
 
 int ib_rdmacg_try_charge(struct ib_rdmacg_object *cg_obj,
 			 struct ib_device *device,
-			 enum rdmacg_resource_type resource_index)
+			 enum rdmacg_resource_type resource_index,
+			 s64 amount)
 {
 	return rdmacg_try_charge(&cg_obj->cg, &device->cg_device,
-				 resource_index);
+				 resource_index, amount);
 }
 EXPORT_SYMBOL(ib_rdmacg_try_charge);
 
 void ib_rdmacg_uncharge(struct ib_rdmacg_object *cg_obj,
 			struct ib_device *device,
-			enum rdmacg_resource_type resource_index)
+			enum rdmacg_resource_type resource_index,
+			s64 amount)
 {
 	rdmacg_uncharge(cg_obj->cg, &device->cg_device,
-			resource_index);
+			resource_index, amount);
 }
 EXPORT_SYMBOL(ib_rdmacg_uncharge);
diff --git a/drivers/infiniband/core/core_priv.h b/drivers/infiniband/core/core_priv.h
index a2c36666e6fc..345356d1e504 100644
--- a/drivers/infiniband/core/core_priv.h
+++ b/drivers/infiniband/core/core_priv.h
@@ -159,11 +159,13 @@ void ib_device_unregister_rdmacg(struct ib_device *device);
 
 int ib_rdmacg_try_charge(struct ib_rdmacg_object *cg_obj,
 			 struct ib_device *device,
-			 enum rdmacg_resource_type resource_index);
+			 enum rdmacg_resource_type resource_index,
+			 s64 amount);
 
 void ib_rdmacg_uncharge(struct ib_rdmacg_object *cg_obj,
 			struct ib_device *device,
-			enum rdmacg_resource_type resource_index);
+			enum rdmacg_resource_type resource_index,
+			 s64 amount);
 #else
 static inline void ib_device_register_rdmacg(struct ib_device *device)
 {
@@ -175,14 +177,16 @@ static inline void ib_device_unregister_rdmacg(struct ib_device *device)
 
 static inline int ib_rdmacg_try_charge(struct ib_rdmacg_object *cg_obj,
 				       struct ib_device *device,
-				       enum rdmacg_resource_type resource_index)
+				       enum rdmacg_resource_type resource_index,
+			       s64 amount)
 {
 	return 0;
 }
 
 static inline void ib_rdmacg_uncharge(struct ib_rdmacg_object *cg_obj,
 				      struct ib_device *device,
-				      enum rdmacg_resource_type resource_index)
+				      enum rdmacg_resource_type resource_index,
+			      s64 amount)
 {
 }
 #endif
diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c
index 5018ec837056..3268285b5478 100644
--- a/drivers/infiniband/core/rdma_core.c
+++ b/drivers/infiniband/core/rdma_core.c
@@ -437,7 +437,7 @@ alloc_begin_idr_uobject(const struct uverbs_api_object *obj,
 		goto uobj_put;
 
 	ret = ib_rdmacg_try_charge(&uobj->cg_obj, uobj->context->device,
-				   RDMACG_RESOURCE_HCA_OBJECT);
+				   RDMACG_RESOURCE_HCA_OBJECT, 1);
 	if (ret)
 		goto remove;
 
@@ -526,7 +526,7 @@ struct ib_uobject *rdma_alloc_begin_uobject(const struct uverbs_api_object *obj,
 static void alloc_abort_idr_uobject(struct ib_uobject *uobj)
 {
 	ib_rdmacg_uncharge(&uobj->cg_obj, uobj->context->device,
-			   RDMACG_RESOURCE_HCA_OBJECT);
+			   RDMACG_RESOURCE_HCA_OBJECT, 1);
 
 	xa_erase(&uobj->ufile->idr, uobj->id);
 }
@@ -547,7 +547,7 @@ static int __must_check destroy_hw_idr_uobject(struct ib_uobject *uobj,
 		return 0;
 
 	ib_rdmacg_uncharge(&uobj->cg_obj, uobj->context->device,
-			   RDMACG_RESOURCE_HCA_OBJECT);
+			   RDMACG_RESOURCE_HCA_OBJECT, 1);
 
 	return 0;
 }
@@ -878,7 +878,7 @@ static void ufile_destroy_ucontext(struct ib_uverbs_file *ufile,
 	}
 
 	ib_rdmacg_uncharge(&ucontext->cg_obj, ib_dev,
-			   RDMACG_RESOURCE_HCA_HANDLE);
+			   RDMACG_RESOURCE_HCA_HANDLE, 1);
 
 	rdma_restrack_del(&ucontext->res);
 
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 91a62d2ade4d..9540ac180711 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -234,7 +234,7 @@ int ib_init_ucontext(struct uverbs_attr_bundle *attrs)
 	}
 
 	ret = ib_rdmacg_try_charge(&ucontext->cg_obj, ucontext->device,
-				   RDMACG_RESOURCE_HCA_HANDLE);
+				   RDMACG_RESOURCE_HCA_HANDLE, 1);
 	if (ret)
 		goto err;
 
@@ -273,7 +273,7 @@ int ib_init_ucontext(struct uverbs_attr_bundle *attrs)
 
 err_uncharge:
 	ib_rdmacg_uncharge(&ucontext->cg_obj, ucontext->device,
-			   RDMACG_RESOURCE_HCA_HANDLE);
+			   RDMACG_RESOURCE_HCA_HANDLE, 1);
 err:
 	mutex_unlock(&file->ucontext_lock);
 	up_read(&file->hw_destroy_rwsem);
diff --git a/include/linux/cgroup_rdma.h b/include/linux/cgroup_rdma.h
index 404e746552ca..7146cefa95a6 100644
--- a/include/linux/cgroup_rdma.h
+++ b/include/linux/cgroup_rdma.h
@@ -7,6 +7,7 @@
 #define _CGROUP_RDMA_H
 
 #include <linux/cgroup.h>
+#include <linux/types.h>
 
 enum rdmacg_resource_type {
 	RDMACG_RESOURCE_HCA_HANDLE,
@@ -46,9 +47,11 @@ void rdmacg_unregister_device(struct rdmacg_device *device);
 /* APIs for RDMA/IB stack to charge/uncharge pool specific resources */
 int rdmacg_try_charge(struct rdma_cgroup **rdmacg,
 		      struct rdmacg_device *device,
-		      enum rdmacg_resource_type index);
+		      enum rdmacg_resource_type index,
+		      s64 amount);
 void rdmacg_uncharge(struct rdma_cgroup *cg,
 		     struct rdmacg_device *device,
-		     enum rdmacg_resource_type index);
+		     enum rdmacg_resource_type index,
+		     s64 amount);
 #endif	/* CONFIG_CGROUP_RDMA */
 #endif	/* _CGROUP_RDMA_H */
diff --git a/kernel/cgroup/rdma.c b/kernel/cgroup/rdma.c
index 5e82a03b3270..519f7f537223 100644
--- a/kernel/cgroup/rdma.c
+++ b/kernel/cgroup/rdma.c
@@ -59,9 +59,9 @@ static char const *rdmacg_resource_names[] = {
 
 /* resource tracker for each resource of rdma cgroup */
 struct rdmacg_resource {
-	int max;
-	int usage;
-	int peak;
+	s64 max;
+	s64 usage;
+	s64 peak;
 };
 
 /*
@@ -105,13 +105,13 @@ static inline struct rdma_cgroup *get_current_rdmacg(void)
 }
 
 static void set_resource_limit(struct rdmacg_resource_pool *rpool,
-			       int index, int new_max)
+			       int index, s64 new_max)
 {
-	if (new_max == S32_MAX) {
-		if (rpool->resources[index].max != S32_MAX)
+	if (new_max == S64_MAX) {
+		if (rpool->resources[index].max != S64_MAX)
 			rpool->num_max_cnt++;
 	} else {
-		if (rpool->resources[index].max == S32_MAX)
+		if (rpool->resources[index].max == S64_MAX)
 			rpool->num_max_cnt--;
 	}
 	rpool->resources[index].max = new_max;
@@ -122,7 +122,7 @@ static void set_all_resource_max_limit(struct rdmacg_resource_pool *rpool)
 	int i;
 
 	for (i = 0; i < RDMACG_RESOURCE_MAX; i++)
-		set_resource_limit(rpool, i, S32_MAX);
+		set_resource_limit(rpool, i, S64_MAX);
 }
 
 static void free_cg_rpool_locked(struct rdmacg_resource_pool *rpool)
@@ -206,7 +206,8 @@ get_cg_rpool_locked(struct rdma_cgroup *cg, struct rdmacg_device *device)
 static void
 uncharge_cg_locked(struct rdma_cgroup *cg,
 		   struct rdmacg_device *device,
-		   enum rdmacg_resource_type index)
+		   enum rdmacg_resource_type index,
+		   s64 amount)
 {
 	struct rdmacg_resource_pool *rpool;
 
@@ -222,7 +223,7 @@ uncharge_cg_locked(struct rdma_cgroup *cg,
 		return;
 	}
 
-	rpool->resources[index].usage--;
+	rpool->resources[index].usage -= amount;
 
 	/*
 	 * A negative count (or overflow) is invalid,
@@ -307,14 +308,15 @@ static void rdmacg_event_locked(struct rdma_cgroup *cg,
 static void rdmacg_uncharge_hierarchy(struct rdma_cgroup *cg,
 				     struct rdmacg_device *device,
 				     struct rdma_cgroup *stop_cg,
-				     enum rdmacg_resource_type index)
+				     enum rdmacg_resource_type index,
+				     s64 amount)
 {
 	struct rdma_cgroup *p;
 
 	mutex_lock(&rdmacg_mutex);
 
 	for (p = cg; p != stop_cg; p = parent_rdmacg(p))
-		uncharge_cg_locked(p, device, index);
+		uncharge_cg_locked(p, device, index, amount);
 
 	mutex_unlock(&rdmacg_mutex);
 
@@ -329,12 +331,13 @@ static void rdmacg_uncharge_hierarchy(struct rdma_cgroup *cg,
  */
 void rdmacg_uncharge(struct rdma_cgroup *cg,
 		     struct rdmacg_device *device,
-		     enum rdmacg_resource_type index)
+		     enum rdmacg_resource_type index,
+		     s64 amount)
 {
 	if (index >= RDMACG_RESOURCE_MAX)
 		return;
 
-	rdmacg_uncharge_hierarchy(cg, device, NULL, index);
+	rdmacg_uncharge_hierarchy(cg, device, NULL, index, amount);
 }
 EXPORT_SYMBOL(rdmacg_uncharge);
 
@@ -343,6 +346,7 @@ EXPORT_SYMBOL(rdmacg_uncharge);
  * @rdmacg: pointer to rdma cgroup which will own this resource
  * @device: pointer to rdmacg device
  * @index: index of the resource to charge in cgroup (resource pool)
+ * @amount: amount to charge
  *
  * This function follows charging resource in hierarchical way.
  * It will fail if the charge would cause the new value to exceed the
@@ -361,7 +365,8 @@ EXPORT_SYMBOL(rdmacg_uncharge);
  */
 int rdmacg_try_charge(struct rdma_cgroup **rdmacg,
 		      struct rdmacg_device *device,
-		      enum rdmacg_resource_type index)
+		      enum rdmacg_resource_type index,
+		      s64 amount)
 {
 	struct rdma_cgroup *cg, *p;
 	struct rdmacg_resource_pool *rpool;
@@ -371,6 +376,9 @@ int rdmacg_try_charge(struct rdma_cgroup **rdmacg,
 	if (index >= RDMACG_RESOURCE_MAX)
 		return -EINVAL;
 
+	if (amount <= 0)
+		return -EINVAL;
+
 	/*
 	 * hold on to css, as cgroup can be removed but resource
 	 * accounting happens on css.
@@ -384,8 +392,9 @@ int rdmacg_try_charge(struct rdma_cgroup **rdmacg,
 			ret = PTR_ERR(rpool);
 			goto err;
 		} else {
-			new = (s64)rpool->resources[index].usage + 1;
-			if (new > rpool->resources[index].max) {
+			new = rpool->resources[index].usage + amount;
+			if (new < rpool->resources[index].usage ||
+			    new > rpool->resources[index].max) {
 				ret = -EAGAIN;
 				goto err;
 			} else {
@@ -409,7 +418,7 @@ int rdmacg_try_charge(struct rdma_cgroup **rdmacg,
 	if (ret == -EAGAIN)
 		rdmacg_event_locked(cg, p, device, index);
 	mutex_unlock(&rdmacg_mutex);
-	rdmacg_uncharge_hierarchy(cg, device, p, index);
+	rdmacg_uncharge_hierarchy(cg, device, p, index, amount);
 	return ret;
 }
 EXPORT_SYMBOL(rdmacg_try_charge);
@@ -477,6 +486,25 @@ static struct rdmacg_device *rdmacg_get_device_locked(const char *name)
 	return NULL;
 }
 
+static int match_s64(substring_t *s, s64 *result)
+{
+	char *buf;
+	int ret;
+	s64 val;
+
+	buf = kmemdup_nul(s->from, s->to - s->from, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+	ret = kstrtoll(buf, 0, &val);
+	kfree(buf);
+	if (ret)
+		return ret;
+	if (val < 0)
+		return -EINVAL;
+	*result = val;
+	return 0;
+}
+
 static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 				       char *buf, size_t nbytes, loff_t off)
 {
@@ -486,7 +514,7 @@ static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 	struct rdmacg_device *device;
 	char *options = strstrip(buf);
 	char *p;
-	int *new_limits;
+	s64 *new_limits;
 	unsigned long enables = 0;
 	int i = 0, ret = 0;
 
@@ -497,7 +525,7 @@ static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 		goto err;
 	}
 
-	new_limits = kzalloc_objs(int, RDMACG_RESOURCE_MAX);
+	new_limits = kcalloc(RDMACG_RESOURCE_MAX, sizeof(s64), GFP_KERNEL);
 	if (!new_limits) {
 		ret = -ENOMEM;
 		goto err;
@@ -506,7 +534,8 @@ static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 	/* parse resource limit tokens */
 	while ((p = strsep(&options, " \t\n"))) {
 		substring_t args[MAX_OPT_ARGS];
-		int tok, intval;
+		int tok;
+		s64 intval;
 
 		if (!*p)
 			continue;
@@ -514,7 +543,7 @@ static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 		tok = match_token(p, rdmacg_limit_tokens, args);
 		switch (tok) {
 		case RDMACG_HCA_HANDLE_VAL:
-			if (match_int(&args[0], &intval) || intval < 0) {
+			if (match_s64(&args[0], &intval)) {
 				ret = -EINVAL;
 				goto parse_err;
 			}
@@ -522,11 +551,11 @@ static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 			enables |= BIT(RDMACG_RESOURCE_HCA_HANDLE);
 			break;
 		case RDMACG_HCA_HANDLE_MAX:
-			new_limits[RDMACG_RESOURCE_HCA_HANDLE] = S32_MAX;
+			new_limits[RDMACG_RESOURCE_HCA_HANDLE] = S64_MAX;
 			enables |= BIT(RDMACG_RESOURCE_HCA_HANDLE);
 			break;
 		case RDMACG_HCA_OBJECT_VAL:
-			if (match_int(&args[0], &intval) || intval < 0) {
+			if (match_s64(&args[0], &intval)) {
 				ret = -EINVAL;
 				goto parse_err;
 			}
@@ -534,7 +563,7 @@ static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 			enables |= BIT(RDMACG_RESOURCE_HCA_OBJECT);
 			break;
 		case RDMACG_HCA_OBJECT_MAX:
-			new_limits[RDMACG_RESOURCE_HCA_OBJECT] = S32_MAX;
+			new_limits[RDMACG_RESOURCE_HCA_OBJECT] = S64_MAX;
 			enables |= BIT(RDMACG_RESOURCE_HCA_OBJECT);
 			break;
 		default:
@@ -588,7 +617,7 @@ static void print_rpool_values(struct seq_file *sf,
 {
 	enum rdmacg_file_type sf_type;
 	int i;
-	u32 value;
+	s64 value;
 
 	sf_type = seq_cft(sf)->private;
 
@@ -599,7 +628,7 @@ static void print_rpool_values(struct seq_file *sf,
 			if (rpool)
 				value = rpool->resources[i].max;
 			else
-				value = S32_MAX;
+				value = S64_MAX;
 		} else if (sf_type == RDMACG_RESOURCE_TYPE_PEAK) {
 			value = rpool ? rpool->resources[i].peak : 0;
 		} else {
@@ -609,10 +638,10 @@ static void print_rpool_values(struct seq_file *sf,
 				value = 0;
 		}
 
-		if (value == S32_MAX)
+		if (value == S64_MAX)
 			seq_puts(sf, RDMACG_MAX_STR);
 		else
-			seq_printf(sf, "%d", value);
+			seq_printf(sf, "%lld", value);
 		seq_putc(sf, ' ');
 	}
 }
-- 
2.43.0

[PATCH rdma-next v2 2/3] cgroup/rdma: add MR memory size resource tracking

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

Add RDMACG_RESOURCE_MR_MEM so that the cumulative memory size of
registered Memory Regions can be tracked and limited independently
from the aggregate hca_object counter.

Unlike count-based resources (hca_handle, hca_object) which are
charged in the generic IDR allocation path, MR_MEM is byte-based
and must be charged after the MR length is known.  Charge in the
uverbs MR registration handlers (ioctl and legacy), and uncharge
in the generic destroy paths (alloc_abort_idr_uobject,
destroy_hw_idr_uobject).

Store the charged byte count in uobj->rdmacg_mr_mem_bytes so that
the destroy path knows how much to uncharge.

Semantic notes
~~~~~~~~~~~~~~

mr_mem is not page-level ownership tracking - it is object-based
accounting tied to the MR lifetime:

  - charged at MR registration time
  - uncharged at MR destruction time
  - the charge lives with the MR's creating cgroup for the entire
    lifetime of the MR object

This model intentionally defines accounting semantics around MR
object lifetime rather than page ownership:

1. fork(): fork() does not duplicate MR objects.  Even though the
   child inherits the uverbs fd and can access the parent's ucontext,
   the MR remains a single kernel object.  The charge is tied to the
   MR object, not to the number of processes that can reach it, so
   no splitting or re-accounting is needed.

2. Cgroup migration: mr_mem follows the same semantics as the existing
   hca_object - charge at creation time against the invoking task's
   cgroup, uncharge at destruction time.  The RDMA cgroup does not
   implement can_attach/attach callbacks today, so charges do not
   migrate with the task.  This is a known limitation that applies
   equally to hca_handle and hca_object.  mr_mem does not introduce
   any new complication here.

3. Overlap with memory cgroup: mr_mem does not count process memory
   usage - it represents a per-device DMA registration budget: how
   much memory can this cgroup register through a given HCA.  This is
   a different dimension from what memory cgroup tracks.  An
   administrator might set mr_mem limits differently per device, which
   memory cgroup cannot express.

   In particular, mr_mem tracks the registered memory range associated
   with the MR rather than exact dynamically pinned pages (e.g. for
   ODP MRs).  This is a stable, policy-oriented approximation of
   registration footprint - not an attempt at precise physical page
   accounting.

Guard against u64-to-s64 overflow by rejecting MR lengths that
exceed S64_MAX at each registration site.

Handle MR reregistration (IB_USER_VERBS_CMD_REREG_MR with
IB_MR_REREG_TRANS) by computing the delta between old and new
lengths and charging or uncharging the difference.  When the driver
creates a new HW object (new_mr != NULL), the full new length is
charged to the new uobj and the old uobj's mr_mem is released
through the existing rdma_assign_uobject -> destroy_hw_idr_uobject
-> rdmacg_uncharge_uobj path.

Enable MR memory limits:

  echo "mlx5_0 mr_mem=1073741824" > rdma.max

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 drivers/infiniband/core/rdma_core.c           | 14 ++++-
 drivers/infiniband/core/uverbs_cmd.c          | 57 +++++++++++++++++++
 drivers/infiniband/core/uverbs_std_types_mr.c | 37 ++++++++++++
 include/linux/cgroup_rdma.h                   |  1 +
 include/rdma/ib_verbs.h                       |  1 +
 kernel/cgroup/rdma.c                          | 21 ++++++-
 6 files changed, 126 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c
index 3268285b5478..a540cef6bb67 100644
--- a/drivers/infiniband/core/rdma_core.c
+++ b/drivers/infiniband/core/rdma_core.c
@@ -523,10 +523,19 @@ struct ib_uobject *rdma_alloc_begin_uobject(const struct uverbs_api_object *obj,
 	return ret;
 }
 
-static void alloc_abort_idr_uobject(struct ib_uobject *uobj)
+static void rdmacg_uncharge_uobj(struct ib_uobject *uobj)
 {
 	ib_rdmacg_uncharge(&uobj->cg_obj, uobj->context->device,
 			   RDMACG_RESOURCE_HCA_OBJECT, 1);
+	if (uobj->rdmacg_mr_mem_bytes)
+		ib_rdmacg_uncharge(&uobj->cg_obj, uobj->context->device,
+				   RDMACG_RESOURCE_MR_MEM,
+				   uobj->rdmacg_mr_mem_bytes);
+}
+
+static void alloc_abort_idr_uobject(struct ib_uobject *uobj)
+{
+	rdmacg_uncharge_uobj(uobj);
 
 	xa_erase(&uobj->ufile->idr, uobj->id);
 }
@@ -546,8 +555,7 @@ static int __must_check destroy_hw_idr_uobject(struct ib_uobject *uobj,
 	if (why == RDMA_REMOVE_ABORT)
 		return 0;
 
-	ib_rdmacg_uncharge(&uobj->cg_obj, uobj->context->device,
-			   RDMACG_RESOURCE_HCA_OBJECT, 1);
+	rdmacg_uncharge_uobj(uobj);
 
 	return 0;
 }
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 9540ac180711..901de117c808 100644
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -752,6 +752,17 @@ static int ib_uverbs_reg_mr(struct uverbs_attr_bundle *attrs)
 
 	uobj->object = mr;
 	uobj_put_obj_read(pd);
+
+	if (cmd.length > S64_MAX)
+		goto err_free;
+	if (cmd.length) {
+		ret = ib_rdmacg_try_charge(&uobj->cg_obj, uobj->context->device,
+					   RDMACG_RESOURCE_MR_MEM, cmd.length);
+		if (ret)
+			goto err_dereg;
+		uobj->rdmacg_mr_mem_bytes = cmd.length;
+	}
+
 	uobj_finalize_uobj_create(uobj, attrs);
 
 	resp.lkey = mr->lkey;
@@ -759,6 +770,8 @@ static int ib_uverbs_reg_mr(struct uverbs_attr_bundle *attrs)
 	resp.mr_handle = uobj->id;
 	return uverbs_response(attrs, &resp, sizeof(resp));
 
+err_dereg:
+	ib_dereg_mr_user(mr, &attrs->driver_udata);
 err_put:
 	uobj_put_obj_read(pd);
 err_free:
@@ -854,6 +867,20 @@ static int ib_uverbs_rereg_mr(struct uverbs_attr_bundle *attrs)
 		rdma_restrack_set_name(&new_mr->res, NULL);
 		rdma_restrack_add(&new_mr->res);
 
+		if ((cmd.flags & IB_MR_REREG_TRANS) && cmd.length) {
+			if (cmd.length > S64_MAX) {
+				ret = -EINVAL;
+				goto err_rereg_new_mr;
+			}
+			ret = ib_rdmacg_try_charge(&new_uobj->cg_obj,
+						   new_uobj->context->device,
+						   RDMACG_RESOURCE_MR_MEM,
+						   cmd.length);
+			if (ret)
+				goto err_rereg_new_mr;
+			new_uobj->rdmacg_mr_mem_bytes = cmd.length;
+		}
+
 		/*
 		 * The new uobj for the new HW object is put into the same spot
 		 * in the IDR and the old uobj & HW object is deleted.
@@ -871,6 +898,31 @@ static int ib_uverbs_rereg_mr(struct uverbs_attr_bundle *attrs)
 			atomic_inc(&new_pd->usecnt);
 		}
 		if (cmd.flags & IB_MR_REREG_TRANS) {
+			s64 delta;
+
+			if (cmd.length > S64_MAX) {
+				ret = -EINVAL;
+				goto put_new_uobj;
+			}
+			delta = (s64)cmd.length -
+				(s64)uobj->rdmacg_mr_mem_bytes;
+
+			if (delta > 0) {
+				ret = ib_rdmacg_try_charge(
+					&uobj->cg_obj,
+					uobj->context->device,
+					RDMACG_RESOURCE_MR_MEM,
+					delta);
+				if (ret)
+					goto put_new_uobj;
+			} else if (delta < 0) {
+				ib_rdmacg_uncharge(
+					&uobj->cg_obj,
+					uobj->context->device,
+					RDMACG_RESOURCE_MR_MEM,
+					-delta);
+			}
+			uobj->rdmacg_mr_mem_bytes = cmd.length;
 			mr->iova = cmd.hca_va;
 			mr->length = cmd.length;
 		}
@@ -887,6 +939,11 @@ static int ib_uverbs_rereg_mr(struct uverbs_attr_bundle *attrs)
 put_new_uobj:
 	if (new_uobj)
 		uobj_alloc_abort(new_uobj, attrs);
+err_rereg_new_mr:
+	if (new_uobj) {
+		rdma_alloc_abort_uobject(new_uobj, attrs, true);
+		new_uobj = NULL;
+	}
 put_uobj_pd:
 	if (cmd.flags & IB_MR_REREG_PD)
 		uobj_put_obj_read(new_pd);
diff --git a/drivers/infiniband/core/uverbs_std_types_mr.c b/drivers/infiniband/core/uverbs_std_types_mr.c
index 570b9656801d..3989ff2d282b 100644
--- a/drivers/infiniband/core/uverbs_std_types_mr.c
+++ b/drivers/infiniband/core/uverbs_std_types_mr.c
@@ -32,6 +32,7 @@
  */
 
 #include "rdma_core.h"
+#include "core_priv.h"
 #include "uverbs.h"
 #include <rdma/uverbs_std_types.h>
 #include "restrack.h"
@@ -140,6 +141,18 @@ static int UVERBS_HANDLER(UVERBS_METHOD_DM_MR_REG)(
 	rdma_restrack_set_name(&mr->res, NULL);
 	rdma_restrack_add(&mr->res);
 	uobj->object = mr;
+	if (attr.length > S64_MAX)
+		return -EINVAL;
+
+	if (attr.length) {
+		ret = ib_rdmacg_try_charge(&uobj->cg_obj, uobj->context->device,
+					   RDMACG_RESOURCE_MR_MEM, attr.length);
+		if (ret) {
+			ib_dereg_mr_user(mr, &attrs->driver_udata);
+			return ret;
+		}
+		uobj->rdmacg_mr_mem_bytes = attr.length;
+	}
 
 	uverbs_finalize_uobj_create(attrs, UVERBS_ATTR_REG_DM_MR_HANDLE);
 
@@ -254,6 +267,18 @@ static int UVERBS_HANDLER(UVERBS_METHOD_REG_DMABUF_MR)(
 	rdma_restrack_add(&mr->res);
 	uobj->object = mr;
 
+	if (length > S64_MAX)
+		return -EINVAL;
+	if (length) {
+		ret = ib_rdmacg_try_charge(&uobj->cg_obj, uobj->context->device,
+					   RDMACG_RESOURCE_MR_MEM, length);
+		if (ret) {
+			ib_dereg_mr_user(mr, &attrs->driver_udata);
+			return ret;
+		}
+		uobj->rdmacg_mr_mem_bytes = length;
+	}
+
 	uverbs_finalize_uobj_create(attrs, UVERBS_ATTR_REG_DMABUF_MR_HANDLE);
 
 	ret = uverbs_copy_to(attrs, UVERBS_ATTR_REG_DMABUF_MR_RESP_LKEY,
@@ -383,6 +408,18 @@ static int UVERBS_HANDLER(UVERBS_METHOD_REG_MR)(
 	rdma_restrack_add(&mr->res);
 	uobj->object = mr;
 
+	if (length > S64_MAX)
+		return -EINVAL;
+	if (length) {
+		ret = ib_rdmacg_try_charge(&uobj->cg_obj, uobj->context->device,
+					   RDMACG_RESOURCE_MR_MEM, length);
+		if (ret) {
+			ib_dereg_mr_user(mr, &attrs->driver_udata);
+			return ret;
+		}
+		uobj->rdmacg_mr_mem_bytes = length;
+	}
+
 	uverbs_finalize_uobj_create(attrs, UVERBS_ATTR_REG_MR_HANDLE);
 
 	ret = uverbs_copy_to(attrs, UVERBS_ATTR_REG_MR_RESP_LKEY,
diff --git a/include/linux/cgroup_rdma.h b/include/linux/cgroup_rdma.h
index 7146cefa95a6..2c8fb1ebb1a9 100644
--- a/include/linux/cgroup_rdma.h
+++ b/include/linux/cgroup_rdma.h
@@ -12,6 +12,7 @@
 enum rdmacg_resource_type {
 	RDMACG_RESOURCE_HCA_HANDLE,
 	RDMACG_RESOURCE_HCA_OBJECT,
+	RDMACG_RESOURCE_MR_MEM,
 	RDMACG_RESOURCE_MAX,
 };
 
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 9dd76f489a0b..c7dcd5d085fb 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -1569,6 +1569,7 @@ struct ib_uobject {
 	void		       *object;		/* containing object */
 	struct list_head	list;		/* link to context's list */
 	struct ib_rdmacg_object	cg_obj;		/* rdmacg object */
+	s64			rdmacg_mr_mem_bytes; /* charged MR memory size */
 	int			id;		/* index into kernel idr */
 	struct kref		ref;
 	atomic_t		usecnt;		/* protects exclusive access */
diff --git a/kernel/cgroup/rdma.c b/kernel/cgroup/rdma.c
index 519f7f537223..ebfc5721c098 100644
--- a/kernel/cgroup/rdma.c
+++ b/kernel/cgroup/rdma.c
@@ -23,14 +23,18 @@ enum rdmacg_limit_tokens {
 	RDMACG_HCA_HANDLE_MAX,
 	RDMACG_HCA_OBJECT_VAL,
 	RDMACG_HCA_OBJECT_MAX,
+	RDMACG_MR_MEM_VAL,
+	RDMACG_MR_MEM_MAX,
 	NR_RDMACG_LIMIT_TOKENS,
 };
 
 static const match_table_t rdmacg_limit_tokens = {
-	{ RDMACG_HCA_HANDLE_VAL,	"hca_handle=%d"	},
+	{ RDMACG_HCA_HANDLE_VAL,	"hca_handle=%d"		},
 	{ RDMACG_HCA_HANDLE_MAX,	"hca_handle=max"	},
-	{ RDMACG_HCA_OBJECT_VAL,	"hca_object=%d"	},
+	{ RDMACG_HCA_OBJECT_VAL,	"hca_object=%d"		},
 	{ RDMACG_HCA_OBJECT_MAX,	"hca_object=max"	},
+	{ RDMACG_MR_MEM_VAL,		"mr_mem=%d"		},
+	{ RDMACG_MR_MEM_MAX,		"mr_mem=max"		},
 	{ NR_RDMACG_LIMIT_TOKENS,	NULL			},
 };
 
@@ -55,6 +59,7 @@ enum rdmacg_file_type {
 static char const *rdmacg_resource_names[] = {
 	[RDMACG_RESOURCE_HCA_HANDLE]	= "hca_handle",
 	[RDMACG_RESOURCE_HCA_OBJECT]	= "hca_object",
+	[RDMACG_RESOURCE_MR_MEM]	= "mr_mem",
 };
 
 /* resource tracker for each resource of rdma cgroup */
@@ -566,6 +571,18 @@ static ssize_t rdmacg_resource_set_max(struct kernfs_open_file *of,
 			new_limits[RDMACG_RESOURCE_HCA_OBJECT] = S64_MAX;
 			enables |= BIT(RDMACG_RESOURCE_HCA_OBJECT);
 			break;
+		case RDMACG_MR_MEM_VAL:
+			if (match_s64(&args[0], &intval)) {
+				ret = -EINVAL;
+				goto parse_err;
+			}
+			new_limits[RDMACG_RESOURCE_MR_MEM] = intval;
+			enables |= BIT(RDMACG_RESOURCE_MR_MEM);
+			break;
+		case RDMACG_MR_MEM_MAX:
+			new_limits[RDMACG_RESOURCE_MR_MEM] = S64_MAX;
+			enables |= BIT(RDMACG_RESOURCE_MR_MEM);
+			break;
 		default:
 			ret = -EINVAL;
 			goto parse_err;
-- 
2.43.0

[PATCH rdma-next v2 3/3] cgroup/rdma: update cgroup resource list for MR_MEM

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

The RDMA cgroup now supports MR memory size tracking via the new
mr_mem resource.  Update the cgroup-v2 documentation to describe
the new resource and revise the usage examples accordingly.

The mr_mem resource tracks the cumulative size of memory registered
through Memory Regions per device per cgroup, providing a DMA
registration budget that is orthogonal to the existing hca_object
counter.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 Documentation/admin-guide/cgroup-v2.rst | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 993446ab66d0..08d80e6f79ec 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2766,15 +2766,16 @@ RDMA Interface Files
 
 	The following nested keys are defined.
 
-	  ==========	=============================
+	  ==========	================================================
 	  hca_handle	Maximum number of HCA Handles
 	  hca_object 	Maximum number of HCA Objects
-	  ==========	=============================
+	  mr_mem	Maximum cumulative MR memory size in bytes
+	  ==========	================================================
 
 	An example for mlx4 and ocrdma device follows::
 
-	  mlx4_0 hca_handle=2 hca_object=2000
-	  ocrdma1 hca_handle=3 hca_object=max
+	  mlx4_0 hca_handle=2 hca_object=2000 mr_mem=1073741824
+	  ocrdma1 hca_handle=3 hca_object=max mr_mem=max
 
   rdma.current
 	A read-only file that describes current resource usage.
@@ -2782,8 +2783,8 @@ RDMA Interface Files
 
 	An example for mlx4 and ocrdma device follows::
 
-	  mlx4_0 hca_handle=1 hca_object=20
-	  ocrdma1 hca_handle=1 hca_object=23
+	  mlx4_0 hca_handle=1 hca_object=20 mr_mem=1048576
+	  ocrdma1 hca_handle=1 hca_object=23 mr_mem=0
 
   rdma.peak
 	A read-only nested-keyed file that exists for all the cgroups
@@ -2792,8 +2793,8 @@ RDMA Interface Files
 
 	An example for mlx4 and ocrdma device follows::
 
-	  mlx4_0 hca_handle=1 hca_object=20
-	  ocrdma1 hca_handle=0 hca_object=23
+	  mlx4_0 hca_handle=1 hca_object=20 mr_mem=1048576
+	  ocrdma1 hca_handle=0 hca_object=23 mr_mem=0
 
   rdma.events
 	A read-only nested-keyed file which exists on non-root
@@ -2815,7 +2816,7 @@ RDMA Interface Files
 
 	An example for mlx4 device follows::
 
-	  mlx4_0 hca_handle.max=5 hca_handle.alloc_fail=3 hca_object.max=0 hca_object.alloc_fail=0
+	  mlx4_0 hca_handle.max=5 hca_handle.alloc_fail=3 hca_object.max=0 hca_object.alloc_fail=0 mr_mem.max=0 mr_mem.alloc_fail=0
 
   rdma.events.local
 	Similar to rdma.events but the fields in the file are local
@@ -2836,7 +2837,7 @@ RDMA Interface Files
 
 	An example for mlx4 device follows::
 
-	  mlx4_0 hca_handle.max=5 hca_handle.alloc_fail=0 hca_object.max=0 hca_object.alloc_fail=0
+	  mlx4_0 hca_handle.max=5 hca_handle.alloc_fail=0 hca_object.max=0 hca_object.alloc_fail=0 mr_mem.max=0 mr_mem.alloc_fail=0
 
 DMEM
 ----
-- 
2.43.0

Re: [PATCH rdma-next v2 3/3] cgroup/rdma: update cgroup resource list for MR_MEM

[kernel test robot]

Hi Tao,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tj-cgroup/for-next]
[also build test WARNING on next-20260528]
[cannot apply to linus/master v7.1-rc5]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Tao-Cui/cgroup-rdma-extend-charge-uncharge-API-with-s64-amount-parameter/20260529-171623
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git for-next
patch link:    https://lore.kernel.org/r/20260529090733.2242822-4-cui.tao%40linux.dev
patch subject: [PATCH rdma-next v2 3/3] cgroup/rdma: update cgroup resource list for MR_MEM
config: i386-allnoconfig-bpf (https://download.01.org/0day-ci/archive/20260529/202605291816.15AyhoZE-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260529/202605291816.15AyhoZE-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202605291816.15AyhoZE-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> Warning: kernel/cgroup/rdma.c:210 function parameter 'amount' not described in 'uncharge_cg_locked'
>> Warning: kernel/cgroup/rdma.c:312 function parameter 'amount' not described in 'rdmacg_uncharge_hierarchy'
>> Warning: kernel/cgroup/rdma.c:335 function parameter 'amount' not described in 'rdmacg_uncharge'
>> Warning: kernel/cgroup/rdma.c:210 function parameter 'amount' not described in 'uncharge_cg_locked'
>> Warning: kernel/cgroup/rdma.c:312 function parameter 'amount' not described in 'rdmacg_uncharge_hierarchy'
>> Warning: kernel/cgroup/rdma.c:335 function parameter 'amount' not described in 'rdmacg_uncharge'

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH rdma-next v2 0/3] cgroup/rdma: add MR memory size resource tracking

[Michal Koutný]

[-- Attachment #1: Type: text/plain, Size: 1600 bytes --]

Hi.

On Fri, May 29, 2026 at 05:07:30PM +0800, Tao Cui <cui.tao@linux.dev> wrote:
> The real scarce resource in multi-tenant
> deployments is pinned memory: how much physical memory gets registered
> through MRs.
> ...
> 3. Overlap with memory cgroup: mr_mem does not count process memory
>    usage; it represents a per-device DMA registration budget: the
>    amount of memory this cgroup may register through a given HCA.
>    This is a different dimension from what memory cgroup tracks.  An
>    administrator might set mr_mem limits differently per device, which
>    memory cgroup cannot express.
> 
>    In particular, mr_mem tracks the registered memory range associated
>    with the MR rather than exact dynamically pinned pages (e.g. for
>    ODP MRs).  This is a stable, policy-oriented approximation of
>    registration footprint, not an attempt at precise physical page
>    accounting.

IIUC the pinned memory is regular RAM, i.e. it could be controlled with
memcg as needed. Or is there "physical" limit of what can be assigned to
a single device?

BTW, have a look at [1], it'd be good to converge to similar approach
(the current proposal allows distinguishing whether charging should
include or exempt memcg counting). Also it seems, that the dmem
controller could be a one-stop solution for all DMA charges. Please tell
me if there are any distinguishing factors between RDMA devices' memory
and these dmem memory regions.

Thanks,
Michal


[1] https://lore.kernel.org/r/20260519-cgroup-dmem-memcg-double-charge-v2-0-db4d1407062b@redhat.com/

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 265 bytes --]

Re: [PATCH rdma-next v2 0/3] cgroup/rdma: add MR memory size resource tracking

[yanjun.zhu]

On 5/29/26 2:07 AM, Tao Cui wrote:
> From: Tao Cui <cuitao@kylinos.cn>
> 
> Currently the RDMA cgroup only tracks two aggregate counters:
> hca_handle and hca_object.  The real scarce resource in multi-tenant
> deployments is pinned memory: how much physical memory gets registered
> through MRs.  The existing hca_object counter is too coarse to capture
> this.
> 
> This series adds a single new resource type:
> 
>    - mr_mem  - Cumulative MR memory size in bytes
> 
> The per-object-type counters (qp, mr) from RFC v1 have been removed
> per review feedback [1]: modern NICs pool objects from the same memory
> pool so the distinction between QP count and MR count is not
> meaningful for resource limiting.  hca_object remains sufficient for
> coarse object accounting.
> 
> After this series, an administrator can set limits like:
> 
>      echo "mlx5_0 mr_mem=1073741824" > rdma.max
> 

Hi,

Thanks for the patchset! Introducing `mr_mem` to track and limit pinned
memory size is a very practical enhancement for multi-tenant deployments.

I have a question regarding how this new resource type interacts with
Fast Registration (FRWR / FRMR), which is widely used in production
environments (e.g., NVMe-oF, iSER) to achieve high performance.

As we know, FRWR decouples the MR object allocation (`ib_alloc_mr`) from
the actual memory page mapping (`ib_map_mr_sg`). The creation of FRWR
Memory Regions is often managed via a pre-allocated page pool.

Could you clarify how `mr_mem` accounts for FRWR in the following scenarios?

1. Accounting Granularity: Does `mr_mem` charge the maximum capacity of
    the FRWR object at its allocation time (`ib_alloc_mr`), or does it
    dynamically track the actual mapped bytes during the fast-reg data 
path? If it's the former, it represents a "static maximum budget" per 
pool, which seems more practical for performance.

2. Kernel-space vs Userspace: FRWR pools are frequently allocated by
    kernel-space drivers (like NVMe-oF target/host). If these kernel
    threads are not bound to a specific user cgroup, will their FRWR
    allocations end up in the root cgroup, potentially bypassing the
    per-tenant limits?

Don't you think it would be beneficial to explicitly document or 
consider the FRWR pattern in the design section, given its prevalence in
real-world storage and networking workloads?

Thanks,
Zhu Yanjun

> Design
> ~~~~~~
> 
> mr_mem is not page-level ownership tracking; it is object-based
> accounting tied to the MR lifetime:
> 
>    - charged at MR registration time
>    - uncharged at MR destruction time
>    - the charge is pinned to the cgroup that created the MR for the
>      entire lifetime of the MR object
> 
> This model intentionally defines accounting semantics around MR
> object lifetime rather than page ownership:
> 
> 1. fork(): fork() does not duplicate MR objects.  Even though the
>     child inherits the uverbs fd and can access the parent's ucontext,
>     the MR remains a single kernel object.  The charge is tied to the
>     MR object, not to the number of processes that can reach it, so
>     no splitting or re-accounting is needed.
> 
> 2. Cgroup migration: mr_mem follows the same semantics as the existing
>     hca_object; charge at creation time against the invoking task's
>     cgroup, uncharge at destruction time.  The RDMA cgroup does not
>     implement can_attach/attach callbacks today, so charges do not
>     migrate with the task.  This is a known limitation that applies
>     equally to hca_handle and hca_object.  mr_mem does not introduce
>     any new complication here.
> 
> 3. Overlap with memory cgroup: mr_mem does not count process memory
>     usage; it represents a per-device DMA registration budget: the
>     amount of memory this cgroup may register through a given HCA.
>     This is a different dimension from what memory cgroup tracks.  An
>     administrator might set mr_mem limits differently per device, which
>     memory cgroup cannot express.
> 
>     In particular, mr_mem tracks the registered memory range associated
>     with the MR rather than exact dynamically pinned pages (e.g. for
>     ODP MRs).  This is a stable, policy-oriented approximation of
>     registration footprint, not an attempt at precise physical page
>     accounting.
> 
> Tao Cui (3):
>    cgroup/rdma: extend charge/uncharge API with s64 amount parameter
>    cgroup/rdma: add MR memory size resource tracking
>    cgroup/rdma: update cgroup resource list for MR_MEM
> 
>   Documentation/admin-guide/cgroup-v2.rst       |  21 ++--
>   drivers/infiniband/core/cgroup.c              |  10 +-
>   drivers/infiniband/core/core_priv.h           |  12 +-
>   drivers/infiniband/core/rdma_core.c           |  20 +++-
>   drivers/infiniband/core/uverbs_cmd.c          |  61 +++++++++-
>   drivers/infiniband/core/uverbs_std_types_mr.c |  37 ++++++
>   include/linux/cgroup_rdma.h                   |   8 +-
>   include/rdma/ib_verbs.h                       |   1 +
>   kernel/cgroup/rdma.c                          | 108 +++++++++++++-----
>   9 files changed, 219 insertions(+), 59 deletions(-)
> 
> ---
> Changes from RFC v1:
> 
>    - Removed RDMACG_RESOURCE_QP and RDMACG_RESOURCE_MR per-type
>      counters following review feedback from Jason Gunthorpe [1].
>    - Retained only RDMACG_RESOURCE_MR_MEM as the sole new resource.
>    - Added detailed semantic notes to the commit messages addressing
>      fork(), cgroup migration, and overlap with memory cgroup [2].
>    - Renamed patches to reflect the narrower scope.
> 
> [1] https://lore.kernel.org/all/20260525134314.GI7702@ziepe.ca/
> [2] https://lore.kernel.org/all/20260528075537.2170697-1-cuitao@kylinos.cn/