[PATCH bpf-next v4 0/7] bpf: Reduce memory usage for bpf_global_percpu_ma

[PATCH bpf-next v4 0/7] bpf: Reduce memory usage for bpf_global_percpu_ma

[Yonghong Song]

Currently when a bpf program intends to allocate memory for percpu kptr,
the verifier will call bpf_mem_alloc_init() to prefill all supported
unit sizes and this caused memory consumption very big for large number
of cpus. For example, for 128-cpu system, the total memory consumption
with initial prefill is ~175MB. Things will become worse for systems
with even more cpus.

Patch 1 avoids unnecessary extra percpu memory allocation.
Patch 2 adds objcg to bpf_mem_alloc at init stage so objcg can be
associated with root cgroup and objcg can be passed to later
bpf_mem_alloc_percpu_unit_init().
Patch 3 addresses memory consumption issue by avoiding to prefill
with all unit sizes, i.e. only prefilling with user specified size.
Patch 4 further reduces memory consumption by limiting the
number of prefill entries for percpu memory allocation.
Patch 5 rejects percpu memory allocation with bpf_global_percpu_ma
when allocation size is greater than 512 bytes.
Patch 6 fixed test_bpf_ma test due to Patch 5.
Patch 7 added one test to show the verification failure log message.

Changelogs:
  v3 -> v4:
    . Add objcg to bpf_mem_alloc during init stage.
    . Initialize objcg at init stage but use it in bpf_mem_alloc_percpu_unit_init().
    . Remove check_obj_size() in bpf_mem_alloc_percpu_unit_init().
  v2 -> v3:
    . Clear the bpf_mem_cache if prefill fails.
    . Change test_bpf_ma percpu allocation tests to use bucket_size
      as allocation size instead of bucket_size - 8.
    . Remove __GFP_ZERO flag from __alloc_percpu_gfp() call.
  v1 -> v2:
    . Avoid unnecessary extra percpu memory allocation.
    . Add a separate function to do bpf_global_percpu_ma initialization
    . promote.
    . Promote function static 'sizes' array to file static.
    . Add comments to explain to refill only one item for percpu alloc.

Yonghong Song (7):
  bpf: Avoid unnecessary extra percpu memory allocation
  bpf: Add objcg to bpf_mem_alloc
  bpf: Allow per unit prefill for non-fix-size percpu memory allocator
  bpf: Refill only one percpu element in memalloc
  bpf: Limit up to 512 bytes for bpf_global_percpu_ma allocation
  selftests/bpf: Cope with 512 bytes limit with bpf_global_percpu_ma
  selftests/bpf: Add a selftest with > 512-byte percpu allocation size

 include/linux/bpf.h                           |  2 +-
 include/linux/bpf_mem_alloc.h                 |  8 ++
 kernel/bpf/core.c                             |  8 +-
 kernel/bpf/memalloc.c                         | 90 ++++++++++++++++---
 kernel/bpf/verifier.c                         | 36 ++++----
 .../selftests/bpf/prog_tests/test_bpf_ma.c    | 20 +++--
 .../selftests/bpf/progs/percpu_alloc_fail.c   | 18 ++++
 .../testing/selftests/bpf/progs/test_bpf_ma.c | 34 +++----
 8 files changed, 160 insertions(+), 56 deletions(-)

-- 
2.34.1

[PATCH bpf-next v4 1/7] bpf: Avoid unnecessary extra percpu memory allocation

[Yonghong Song]

Currently, for percpu memory allocation, say if the user
requests allocation size to be 32 bytes, the actually
calculated size will be 40 bytes and it further rounds
to 64 bytes, and eventually 64 bytes are allocated,
wasting 32-byte memory.

Change bpf_mem_alloc() to calculate the cache index
based on the user-provided allocation size so unnecessary
extra memory can be avoided.

Suggested-by: Hou Tao <houtao1@huawei.com>
Acked-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/memalloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 6a51cfe4c2d6..00e101c2a68b 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -871,7 +871,9 @@ void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
 	if (!size)
 		return ZERO_SIZE_PTR;
 
-	idx = bpf_mem_cache_idx(size + LLIST_NODE_SZ);
+	if (!ma->percpu)
+		size += LLIST_NODE_SZ;
+	idx = bpf_mem_cache_idx(size);
 	if (idx < 0)
 		return NULL;
 
-- 
2.34.1

[PATCH bpf-next v4 2/7] bpf: Add objcg to bpf_mem_alloc

[Yonghong Song]

The objcg is a bpf_mem_alloc level property since all bpf_mem_cache's
are with the same objcg. This patch made such a property explicit.
The next patch will use this property to save and restore objcg
for percpu unit allocator.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 include/linux/bpf_mem_alloc.h |  1 +
 kernel/bpf/memalloc.c         | 11 ++++++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h
index bb1223b21308..acef8c808599 100644
--- a/include/linux/bpf_mem_alloc.h
+++ b/include/linux/bpf_mem_alloc.h
@@ -11,6 +11,7 @@ struct bpf_mem_caches;
 struct bpf_mem_alloc {
 	struct bpf_mem_caches __percpu *caches;
 	struct bpf_mem_cache __percpu *cache;
+	struct obj_cgroup *objcg;
 	bool percpu;
 	struct work_struct work;
 };
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 00e101c2a68b..dfde9d9a3e1d 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -544,6 +544,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 		if (memcg_bpf_enabled())
 			objcg = get_obj_cgroup_from_current();
 #endif
+		ma->objcg = objcg;
 		for_each_possible_cpu(cpu) {
 			c = per_cpu_ptr(pc, cpu);
 			c->unit_size = unit_size;
@@ -564,6 +565,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 #ifdef CONFIG_MEMCG_KMEM
 	objcg = get_obj_cgroup_from_current();
 #endif
+	ma->objcg = objcg;
 	for_each_possible_cpu(cpu) {
 		cc = per_cpu_ptr(pcc, cpu);
 		for (i = 0; i < NUM_CACHES; i++) {
@@ -729,9 +731,8 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
 			rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
 			rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
 		}
-		/* objcg is the same across cpus */
-		if (c->objcg)
-			obj_cgroup_put(c->objcg);
+		if (ma->objcg)
+			obj_cgroup_put(ma->objcg);
 		destroy_mem_alloc(ma, rcu_in_progress);
 	}
 	if (ma->caches) {
@@ -747,8 +748,8 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
 				rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
 			}
 		}
-		if (c->objcg)
-			obj_cgroup_put(c->objcg);
+		if (ma->objcg)
+			obj_cgroup_put(ma->objcg);
 		destroy_mem_alloc(ma, rcu_in_progress);
 	}
 }
-- 
2.34.1

[PATCH bpf-next v4 3/7] bpf: Allow per unit prefill for non-fix-size percpu memory allocator

[Yonghong Song]

Commit 41a5db8d8161 ("Add support for non-fix-size percpu mem allocation")
added support for non-fix-size percpu memory allocation.
Such allocation will allocate percpu memory for all buckets on all
cpus and the memory consumption is in the order to quadratic.
For example, let us say, 4 cpus, unit size 16 bytes, so each
cpu has 16 * 4 = 64 bytes, with 4 cpus, total will be 64 * 4 = 256 bytes.
Then let us say, 8 cpus with the same unit size, each cpu
has 16 * 8 = 128 bytes, with 8 cpus, total will be 128 * 8 = 1024 bytes.
So if the number of cpus doubles, the number of memory consumption
will be 4 times. So for a system with large number of cpus, the
memory consumption goes up quickly with quadratic order.
For example, for 4KB percpu allocation, 128 cpus. The total memory
consumption will 4KB * 128 * 128 = 64MB. Things will become
worse if the number of cpus is bigger (e.g., 512, 1024, etc.)

In Commit 41a5db8d8161, the non-fix-size percpu memory allocation is
done in boot time, so for system with large number of cpus, the initial
percpu memory consumption is very visible. For example, for 128 cpu
system, the total percpu memory allocation will be at least
(16 + 32 + 64 + 96 + 128 + 196 + 256 + 512 + 1024 + 2048 + 4096)
  * 128 * 128 = ~138MB.
which is pretty big. It will be even bigger for larger number of cpus.

Note that the current prefill also allocates 4 entries if the unit size
is less than 256. So on top of 138MB memory consumption, this will
add more consumption with
3 * (16 + 32 + 64 + 96 + 128 + 196 + 256) * 128 * 128 = ~38MB.
Next patch will try to reduce this memory consumption.

Later on, Commit 1fda5bb66ad8 ("bpf: Do not allocate percpu memory
at init stage") moved the non-fix-size percpu memory allocation
to bpf verificaiton stage. Once a particular bpf_percpu_obj_new()
is called by bpf program, the memory allocator will try to fill in
the cache with all sizes, causing the same amount of percpu memory
consumption as in the boot stage.

To reduce the initial percpu memory consumption for non-fix-size
percpu memory allocation, instead of filling the cache with all
supported allocation sizes, this patch intends to fill the cache
only for the requested size. As typically users will not use large
percpu data structure, this can save memory significantly.
For example, the allocation size is 64 bytes with 128 cpus.
Then total percpu memory amount will be 64 * 128 * 128 = 1MB,
much less than previous 138MB.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 include/linux/bpf.h           |  2 +-
 include/linux/bpf_mem_alloc.h |  7 ++++
 kernel/bpf/core.c             |  8 +++--
 kernel/bpf/memalloc.c         | 62 ++++++++++++++++++++++++++++++++++-
 kernel/bpf/verifier.c         | 28 +++++++---------
 5 files changed, 85 insertions(+), 22 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5e694934cf37..bd32274561e3 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -61,7 +61,7 @@ extern struct idr btf_idr;
 extern spinlock_t btf_idr_lock;
 extern struct kobject *btf_kobj;
 extern struct bpf_mem_alloc bpf_global_ma, bpf_global_percpu_ma;
-extern bool bpf_global_ma_set;
+extern bool bpf_global_ma_set, bpf_global_percpu_ma_set;
 
 typedef u64 (*bpf_callback_t)(u64, u64, u64, u64, u64);
 typedef int (*bpf_iter_init_seq_priv_t)(void *private_data,
diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h
index acef8c808599..d1403204379e 100644
--- a/include/linux/bpf_mem_alloc.h
+++ b/include/linux/bpf_mem_alloc.h
@@ -22,8 +22,15 @@ struct bpf_mem_alloc {
  * 'size = 0' is for bpf_mem_alloc which manages many fixed-size objects.
  * Alloc and free are done with bpf_mem_{alloc,free}() and the size of
  * the returned object is given by the size argument of bpf_mem_alloc().
+ * If percpu equals true, error will be returned in order to avoid
+ * large memory consumption and the below bpf_mem_alloc_percpu_unit_init()
+ * should be used to do on-demand per-cpu allocation for each size.
  */
 int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu);
+/* Initialize a non-fix-size percpu memory allocator */
+int bpf_mem_alloc_percpu_init(struct bpf_mem_alloc *ma);
+/* The percpu allocation with a specific unit size. */
+int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size);
 void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma);
 
 /* kmalloc/kfree equivalent: */
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5aa6863ac33b..bc93eb7e00c7 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -64,8 +64,8 @@
 #define OFF	insn->off
 #define IMM	insn->imm
 
-struct bpf_mem_alloc bpf_global_ma;
-bool bpf_global_ma_set;
+struct bpf_mem_alloc bpf_global_ma, bpf_global_percpu_ma;
+bool bpf_global_ma_set, bpf_global_percpu_ma_set;
 
 /* No hurry in this branch
  *
@@ -2963,7 +2963,9 @@ static int __init bpf_global_ma_init(void)
 
 	ret = bpf_mem_alloc_init(&bpf_global_ma, 0, false);
 	bpf_global_ma_set = !ret;
-	return ret;
+	ret = bpf_mem_alloc_percpu_init(&bpf_global_percpu_ma);
+	bpf_global_percpu_ma_set = !ret;
+	return !bpf_global_ma_set || !bpf_global_percpu_ma_set;
 }
 late_initcall(bpf_global_ma_init);
 #endif
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index dfde9d9a3e1d..50ab2fecc005 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -121,6 +121,8 @@ struct bpf_mem_caches {
 	struct bpf_mem_cache cache[NUM_CACHES];
 };
 
+static const u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
+
 static struct llist_node notrace *__llist_del_first(struct llist_head *head)
 {
 	struct llist_node *entry, *next;
@@ -520,12 +522,14 @@ static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)
  */
 int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 {
-	static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
 	int cpu, i, err, unit_size, percpu_size = 0;
 	struct bpf_mem_caches *cc, __percpu *pcc;
 	struct bpf_mem_cache *c, __percpu *pc;
 	struct obj_cgroup *objcg = NULL;
 
+	if (percpu && size == 0)
+		return -EINVAL;
+
 	/* room for llist_node and per-cpu pointer */
 	if (percpu)
 		percpu_size = LLIST_NODE_SZ + sizeof(void *);
@@ -545,6 +549,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 			objcg = get_obj_cgroup_from_current();
 #endif
 		ma->objcg = objcg;
+
 		for_each_possible_cpu(cpu) {
 			c = per_cpu_ptr(pc, cpu);
 			c->unit_size = unit_size;
@@ -600,6 +605,61 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
 	return err;
 }
 
+__init int bpf_mem_alloc_percpu_init(struct bpf_mem_alloc *ma)
+{
+	struct bpf_mem_caches __percpu *pcc;
+
+	pcc = __alloc_percpu_gfp(sizeof(struct bpf_mem_caches), 8, GFP_KERNEL);
+	if (!pcc)
+		return -ENOMEM;
+
+	ma->caches = pcc;
+	ma->percpu = true;
+
+#ifdef CONFIG_MEMCG_KMEM
+	ma->objcg = get_obj_cgroup_from_current();
+#else
+	ma->objcg = NULL;
+#endif
+	return 0;
+}
+
+int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size)
+{
+	struct bpf_mem_caches *cc, __percpu *pcc;
+	int cpu, i, unit_size, percpu_size;
+	struct obj_cgroup *objcg;
+	struct bpf_mem_cache *c;
+
+	i = bpf_mem_cache_idx(size);
+	if (i < 0)
+		return -EINVAL;
+
+	/* room for llist_node and per-cpu pointer */
+	percpu_size = LLIST_NODE_SZ + sizeof(void *);
+
+	unit_size = sizes[i];
+	objcg = ma->objcg;
+	pcc = ma->caches;
+
+	for_each_possible_cpu(cpu) {
+		cc = per_cpu_ptr(pcc, cpu);
+		c = &cc->cache[i];
+		if (cpu == 0 && c->unit_size)
+			break;
+
+		c->unit_size = unit_size;
+		c->objcg = objcg;
+		c->percpu_size = percpu_size;
+		c->tgt = c;
+
+		init_refill_work(c);
+		prefill_mem_cache(c, cpu);
+	}
+
+	return 0;
+}
+
 static void drain_mem_cache(struct bpf_mem_cache *c)
 {
 	bool percpu = !!c->percpu_size;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1863826a4ac3..ce62ee0cc8f6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -42,9 +42,6 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = {
 #undef BPF_LINK_TYPE
 };
 
-struct bpf_mem_alloc bpf_global_percpu_ma;
-static bool bpf_global_percpu_ma_set;
-
 /* bpf_check() is a static code analyzer that walks eBPF program
  * instruction by instruction and updates register/stack state.
  * All paths of conditional branches are analyzed until 'bpf_exit' insn.
@@ -12062,20 +12059,6 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 				if (meta.func_id == special_kfunc_list[KF_bpf_obj_new_impl] && !bpf_global_ma_set)
 					return -ENOMEM;
 
-				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
-					if (!bpf_global_percpu_ma_set) {
-						mutex_lock(&bpf_percpu_ma_lock);
-						if (!bpf_global_percpu_ma_set) {
-							err = bpf_mem_alloc_init(&bpf_global_percpu_ma, 0, true);
-							if (!err)
-								bpf_global_percpu_ma_set = true;
-						}
-						mutex_unlock(&bpf_percpu_ma_lock);
-						if (err)
-							return err;
-					}
-				}
-
 				if (((u64)(u32)meta.arg_constant.value) != meta.arg_constant.value) {
 					verbose(env, "local type ID argument must be in range [0, U32_MAX]\n");
 					return -EINVAL;
@@ -12096,6 +12079,17 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 					return -EINVAL;
 				}
 
+				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
+					if (!bpf_global_percpu_ma_set)
+						return -ENOMEM;
+
+					mutex_lock(&bpf_percpu_ma_lock);
+					err = bpf_mem_alloc_percpu_unit_init(&bpf_global_percpu_ma, ret_t->size);
+					mutex_unlock(&bpf_percpu_ma_lock);
+					if (err)
+						return err;
+				}
+
 				struct_meta = btf_find_struct_meta(ret_btf, ret_btf_id);
 				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
 					if (!__btf_type_is_scalar_struct(env, ret_btf, ret_t, 0)) {
-- 
2.34.1

[PATCH bpf-next v4 4/7] bpf: Refill only one percpu element in memalloc

[Yonghong Song]

Typically for percpu map element or data structure, once allocated,
most operations are lookup or in-place update. Deletion are really
rare. Currently, for percpu data strcture, 4 elements will be
refilled if the size is <= 256. Let us just do with one element
for percpu data. For example, for size 256 and 128 cpus, the
potential saving will be 3 * 256 * 128 * 128 = 12MB.

Acked-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/memalloc.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 50ab2fecc005..f37998662146 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -485,11 +485,16 @@ static void init_refill_work(struct bpf_mem_cache *c)
 
 static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
 {
-	/* To avoid consuming memory assume that 1st run of bpf
-	 * prog won't be doing more than 4 map_update_elem from
-	 * irq disabled region
+	int cnt = 1;
+
+	/* To avoid consuming memory, for non-percpu allocation, assume that
+	 * 1st run of bpf prog won't be doing more than 4 map_update_elem from
+	 * irq disabled region if unit size is less than or equal to 256.
+	 * For all other cases, let us just do one allocation.
 	 */
-	alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu), false);
+	if (!c->percpu_size && c->unit_size <= 256)
+		cnt = 4;
+	alloc_bulk(c, cnt, cpu_to_node(cpu), false);
 }
 
 static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)
-- 
2.34.1

[PATCH bpf-next v4 5/7] bpf: Limit up to 512 bytes for bpf_global_percpu_ma allocation

[Yonghong Song]

For percpu data structure allocation with bpf_global_percpu_ma,
the maximum data size is 4K. But for a system with large
number of cpus, bigger data size (e.g., 2K, 4K) might consume
a lot of memory. For example, the percpu memory consumption
with unit size 2K and 1024 cpus will be 2K * 1K * 1k = 2GB
memory.

We should discourage such usage. Let us limit the maximum data
size to be 512 for bpf_global_percpu_ma allocation.

Acked-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/verifier.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ce62ee0cc8f6..039d699a425d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -192,6 +192,8 @@ struct bpf_verifier_stack_elem {
 					  POISON_POINTER_DELTA))
 #define BPF_MAP_PTR(X)		((struct bpf_map *)((X) & ~BPF_MAP_PTR_UNPRIV))
 
+#define BPF_GLOBAL_PERCPU_MA_MAX_SIZE  512
+
 static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx);
 static int release_reference(struct bpf_verifier_env *env, int ref_obj_id);
 static void invalidate_non_owning_refs(struct bpf_verifier_env *env);
@@ -12083,6 +12085,12 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 					if (!bpf_global_percpu_ma_set)
 						return -ENOMEM;
 
+					if (ret_t->size > BPF_GLOBAL_PERCPU_MA_MAX_SIZE) {
+						verbose(env, "bpf_percpu_obj_new type size (%d) is greater than %d\n",
+							ret_t->size, BPF_GLOBAL_PERCPU_MA_MAX_SIZE);
+						return -EINVAL;
+					}
+
 					mutex_lock(&bpf_percpu_ma_lock);
 					err = bpf_mem_alloc_percpu_unit_init(&bpf_global_percpu_ma, ret_t->size);
 					mutex_unlock(&bpf_percpu_ma_lock);
-- 
2.34.1

[PATCH bpf-next v4 6/7] selftests/bpf: Cope with 512 bytes limit with bpf_global_percpu_ma

[Yonghong Song]

In the previous patch, the maximum data size for bpf_global_percpu_ma
is 512 bytes. This breaks selftest test_bpf_ma. The test is adjusted
in two aspects:
  - Since the maximum allowed data size for bpf_global_percpu_ma is
    512, remove all tests beyond that, names sizes 1024, 2048 and 4096.
  - Previously the percpu data size is bucket_size - 8 in order to
    avoid percpu allocation into the next bucket. This patch removed
    such data size adjustment thanks to Patch 1.

Also, a better way to generate BTF type is used than adding
a member to the value struct.

Acked-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 .../selftests/bpf/prog_tests/test_bpf_ma.c    | 20 +++++++----
 .../testing/selftests/bpf/progs/test_bpf_ma.c | 34 +++++++++----------
 2 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/test_bpf_ma.c b/tools/testing/selftests/bpf/prog_tests/test_bpf_ma.c
index d3491a84b3b9..ccae0b31ac6c 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_bpf_ma.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_bpf_ma.c
@@ -14,7 +14,8 @@ static void do_bpf_ma_test(const char *name)
 	struct test_bpf_ma *skel;
 	struct bpf_program *prog;
 	struct btf *btf;
-	int i, err;
+	int i, err, id;
+	char tname[32];
 
 	skel = test_bpf_ma__open();
 	if (!ASSERT_OK_PTR(skel, "open"))
@@ -25,16 +26,21 @@ static void do_bpf_ma_test(const char *name)
 		goto out;
 
 	for (i = 0; i < ARRAY_SIZE(skel->rodata->data_sizes); i++) {
-		char name[32];
-		int id;
-
-		snprintf(name, sizeof(name), "bin_data_%u", skel->rodata->data_sizes[i]);
-		id = btf__find_by_name_kind(btf, name, BTF_KIND_STRUCT);
-		if (!ASSERT_GT(id, 0, "bin_data"))
+		snprintf(tname, sizeof(tname), "bin_data_%u", skel->rodata->data_sizes[i]);
+		id = btf__find_by_name_kind(btf, tname, BTF_KIND_STRUCT);
+		if (!ASSERT_GT(id, 0, tname))
 			goto out;
 		skel->rodata->data_btf_ids[i] = id;
 	}
 
+	for (i = 0; i < ARRAY_SIZE(skel->rodata->percpu_data_sizes); i++) {
+		snprintf(tname, sizeof(tname), "percpu_bin_data_%u", skel->rodata->percpu_data_sizes[i]);
+		id = btf__find_by_name_kind(btf, tname, BTF_KIND_STRUCT);
+		if (!ASSERT_GT(id, 0, tname))
+			goto out;
+		skel->rodata->percpu_data_btf_ids[i] = id;
+	}
+
 	prog = bpf_object__find_program_by_name(skel->obj, name);
 	if (!ASSERT_OK_PTR(prog, "invalid prog name"))
 		goto out;
diff --git a/tools/testing/selftests/bpf/progs/test_bpf_ma.c b/tools/testing/selftests/bpf/progs/test_bpf_ma.c
index b685a4aba6bd..e453a9392e5a 100644
--- a/tools/testing/selftests/bpf/progs/test_bpf_ma.c
+++ b/tools/testing/selftests/bpf/progs/test_bpf_ma.c
@@ -20,6 +20,9 @@ char _license[] SEC("license") = "GPL";
 const unsigned int data_sizes[] = {8, 16, 32, 64, 96, 128, 192, 256, 512, 1024, 2048, 4096};
 const volatile unsigned int data_btf_ids[ARRAY_SIZE(data_sizes)] = {};
 
+const unsigned int percpu_data_sizes[] = {8, 16, 32, 64, 96, 128, 192, 256, 512};
+const volatile unsigned int percpu_data_btf_ids[ARRAY_SIZE(data_sizes)] = {};
+
 int err = 0;
 int pid = 0;
 
@@ -27,10 +30,10 @@ int pid = 0;
 	struct bin_data_##_size { \
 		char data[_size - sizeof(void *)]; \
 	}; \
+	/* See Commit 5d8d6634ccc, force btf generation for type bin_data_##_size */	\
+	struct bin_data_##_size *__bin_data_##_size; \
 	struct map_value_##_size { \
 		struct bin_data_##_size __kptr * data; \
-		/* To emit BTF info for bin_data_xx */ \
-		struct bin_data_##_size not_used; \
 	}; \
 	struct { \
 		__uint(type, BPF_MAP_TYPE_ARRAY); \
@@ -40,8 +43,12 @@ int pid = 0;
 	} array_##_size SEC(".maps")
 
 #define DEFINE_ARRAY_WITH_PERCPU_KPTR(_size) \
+	struct percpu_bin_data_##_size { \
+		char data[_size]; \
+	}; \
+	struct percpu_bin_data_##_size *__percpu_bin_data_##_size; \
 	struct map_value_percpu_##_size { \
-		struct bin_data_##_size __percpu_kptr * data; \
+		struct percpu_bin_data_##_size __percpu_kptr * data; \
 	}; \
 	struct { \
 		__uint(type, BPF_MAP_TYPE_ARRAY); \
@@ -114,7 +121,7 @@ static __always_inline void batch_percpu_alloc(struct bpf_map *map, unsigned int
 			return;
 		}
 		/* per-cpu allocator may not be able to refill in time */
-		new = bpf_percpu_obj_new_impl(data_btf_ids[idx], NULL);
+		new = bpf_percpu_obj_new_impl(percpu_data_btf_ids[idx], NULL);
 		if (!new)
 			continue;
 
@@ -179,7 +186,7 @@ DEFINE_ARRAY_WITH_KPTR(1024);
 DEFINE_ARRAY_WITH_KPTR(2048);
 DEFINE_ARRAY_WITH_KPTR(4096);
 
-/* per-cpu kptr doesn't support bin_data_8 which is a zero-sized array */
+DEFINE_ARRAY_WITH_PERCPU_KPTR(8);
 DEFINE_ARRAY_WITH_PERCPU_KPTR(16);
 DEFINE_ARRAY_WITH_PERCPU_KPTR(32);
 DEFINE_ARRAY_WITH_PERCPU_KPTR(64);
@@ -188,9 +195,6 @@ DEFINE_ARRAY_WITH_PERCPU_KPTR(128);
 DEFINE_ARRAY_WITH_PERCPU_KPTR(192);
 DEFINE_ARRAY_WITH_PERCPU_KPTR(256);
 DEFINE_ARRAY_WITH_PERCPU_KPTR(512);
-DEFINE_ARRAY_WITH_PERCPU_KPTR(1024);
-DEFINE_ARRAY_WITH_PERCPU_KPTR(2048);
-DEFINE_ARRAY_WITH_PERCPU_KPTR(4096);
 
 SEC("?fentry/" SYS_PREFIX "sys_nanosleep")
 int test_batch_alloc_free(void *ctx)
@@ -248,9 +252,10 @@ int test_batch_percpu_alloc_free(void *ctx)
 	if ((u32)bpf_get_current_pid_tgid() != pid)
 		return 0;
 
-	/* Alloc 128 16-bytes per-cpu objects in batch to trigger refilling,
-	 * then free 128 16-bytes per-cpu objects in batch to trigger freeing.
+	/* Alloc 128 8-bytes per-cpu objects in batch to trigger refilling,
+	 * then free 128 8-bytes per-cpu objects in batch to trigger freeing.
 	 */
+	CALL_BATCH_PERCPU_ALLOC_FREE(8, 128, 0);
 	CALL_BATCH_PERCPU_ALLOC_FREE(16, 128, 1);
 	CALL_BATCH_PERCPU_ALLOC_FREE(32, 128, 2);
 	CALL_BATCH_PERCPU_ALLOC_FREE(64, 128, 3);
@@ -259,9 +264,6 @@ int test_batch_percpu_alloc_free(void *ctx)
 	CALL_BATCH_PERCPU_ALLOC_FREE(192, 128, 6);
 	CALL_BATCH_PERCPU_ALLOC_FREE(256, 128, 7);
 	CALL_BATCH_PERCPU_ALLOC_FREE(512, 64, 8);
-	CALL_BATCH_PERCPU_ALLOC_FREE(1024, 32, 9);
-	CALL_BATCH_PERCPU_ALLOC_FREE(2048, 16, 10);
-	CALL_BATCH_PERCPU_ALLOC_FREE(4096, 8, 11);
 
 	return 0;
 }
@@ -272,9 +274,10 @@ int test_percpu_free_through_map_free(void *ctx)
 	if ((u32)bpf_get_current_pid_tgid() != pid)
 		return 0;
 
-	/* Alloc 128 16-bytes per-cpu objects in batch to trigger refilling,
+	/* Alloc 128 8-bytes per-cpu objects in batch to trigger refilling,
 	 * then free these object through map free.
 	 */
+	CALL_BATCH_PERCPU_ALLOC(8, 128, 0);
 	CALL_BATCH_PERCPU_ALLOC(16, 128, 1);
 	CALL_BATCH_PERCPU_ALLOC(32, 128, 2);
 	CALL_BATCH_PERCPU_ALLOC(64, 128, 3);
@@ -283,9 +286,6 @@ int test_percpu_free_through_map_free(void *ctx)
 	CALL_BATCH_PERCPU_ALLOC(192, 128, 6);
 	CALL_BATCH_PERCPU_ALLOC(256, 128, 7);
 	CALL_BATCH_PERCPU_ALLOC(512, 64, 8);
-	CALL_BATCH_PERCPU_ALLOC(1024, 32, 9);
-	CALL_BATCH_PERCPU_ALLOC(2048, 16, 10);
-	CALL_BATCH_PERCPU_ALLOC(4096, 8, 11);
 
 	return 0;
 }
-- 
2.34.1

[PATCH bpf-next v4 7/7] selftests/bpf: Add a selftest with > 512-byte percpu allocation size

[Yonghong Song]

Add a selftest to capture the verification failure when the allocation
size is greater than 512.

Acked-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 .../selftests/bpf/progs/percpu_alloc_fail.c    | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c b/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c
index 1a891d30f1fe..f2b8eb2ff76f 100644
--- a/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c
+++ b/tools/testing/selftests/bpf/progs/percpu_alloc_fail.c
@@ -17,6 +17,10 @@ struct val_with_rb_root_t {
 	struct bpf_spin_lock lock;
 };
 
+struct val_600b_t {
+	char b[600];
+};
+
 struct elem {
 	long sum;
 	struct val_t __percpu_kptr *pc;
@@ -161,4 +165,18 @@ int BPF_PROG(test_array_map_7)
 	return 0;
 }
 
+SEC("?fentry.s/bpf_fentry_test1")
+__failure __msg("bpf_percpu_obj_new type size (600) is greater than 512")
+int BPF_PROG(test_array_map_8)
+{
+	struct val_600b_t __percpu_kptr *p;
+
+	p = bpf_percpu_obj_new(struct val_600b_t);
+	if (!p)
+		return 0;
+
+	bpf_percpu_obj_drop(p);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.34.1

Re: [PATCH bpf-next v4 2/7] bpf: Add objcg to bpf_mem_alloc

[Hou Tao]

On 12/18/2023 2:30 PM, Yonghong Song wrote:
> The objcg is a bpf_mem_alloc level property since all bpf_mem_cache's
> are with the same objcg. This patch made such a property explicit.
> The next patch will use this property to save and restore objcg
> for percpu unit allocator.
>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>

Acked-by: Hou Tao <houtao1@huawei.com>

Re: [PATCH bpf-next v4 3/7] bpf: Allow per unit prefill for non-fix-size percpu memory allocator

[Hou Tao]

On 12/18/2023 2:30 PM, Yonghong Song wrote:
> Commit 41a5db8d8161 ("Add support for non-fix-size percpu mem allocation")
> added support for non-fix-size percpu memory allocation.
> Such allocation will allocate percpu memory for all buckets on all
> cpus and the memory consumption is in the order to quadratic.
> For example, let us say, 4 cpus, unit size 16 bytes, so each
> cpu has 16 * 4 = 64 bytes, with 4 cpus, total will be 64 * 4 = 256 bytes.
> Then let us say, 8 cpus with the same unit size, each cpu
> has 16 * 8 = 128 bytes, with 8 cpus, total will be 128 * 8 = 1024 bytes.
> So if the number of cpus doubles, the number of memory consumption
> will be 4 times. So for a system with large number of cpus, the
> memory consumption goes up quickly with quadratic order.
> For example, for 4KB percpu allocation, 128 cpus. The total memory
> consumption will 4KB * 128 * 128 = 64MB. Things will become
> worse if the number of cpus is bigger (e.g., 512, 1024, etc.)
>
> In Commit 41a5db8d8161, the non-fix-size percpu memory allocation is
> done in boot time, so for system with large number of cpus, the initial
> percpu memory consumption is very visible. For example, for 128 cpu
> system, the total percpu memory allocation will be at least
> (16 + 32 + 64 + 96 + 128 + 196 + 256 + 512 + 1024 + 2048 + 4096)
>   * 128 * 128 = ~138MB.
> which is pretty big. It will be even bigger for larger number of cpus.
>
> Note that the current prefill also allocates 4 entries if the unit size
> is less than 256. So on top of 138MB memory consumption, this will
> add more consumption with
> 3 * (16 + 32 + 64 + 96 + 128 + 196 + 256) * 128 * 128 = ~38MB.
> Next patch will try to reduce this memory consumption.
>
> Later on, Commit 1fda5bb66ad8 ("bpf: Do not allocate percpu memory
> at init stage") moved the non-fix-size percpu memory allocation
> to bpf verificaiton stage. Once a particular bpf_percpu_obj_new()
> is called by bpf program, the memory allocator will try to fill in
> the cache with all sizes, causing the same amount of percpu memory
> consumption as in the boot stage.
>
> To reduce the initial percpu memory consumption for non-fix-size
> percpu memory allocation, instead of filling the cache with all
> supported allocation sizes, this patch intends to fill the cache
> only for the requested size. As typically users will not use large
> percpu data structure, this can save memory significantly.
> For example, the allocation size is 64 bytes with 128 cpus.
> Then total percpu memory amount will be 64 * 128 * 128 = 1MB,
> much less than previous 138MB.
>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>

Acked-by: Hou Tao <houtao1@huawei.com>

Re: [PATCH bpf-next v4 4/7] bpf: Refill only one percpu element in memalloc

[Hou Tao]

Hi,

On 12/18/2023 2:30 PM, Yonghong Song wrote:
> Typically for percpu map element or data structure, once allocated,
> most operations are lookup or in-place update. Deletion are really
> rare. Currently, for percpu data strcture, 4 elements will be
> refilled if the size is <= 256. Let us just do with one element
> for percpu data. For example, for size 256 and 128 cpus, the
> potential saving will be 3 * 256 * 128 * 128 = 12MB.
>
> Acked-by: Hou Tao <houtao1@huawei.com>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---
>  kernel/bpf/memalloc.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
> index 50ab2fecc005..f37998662146 100644
> --- a/kernel/bpf/memalloc.c
> +++ b/kernel/bpf/memalloc.c
> @@ -485,11 +485,16 @@ static void init_refill_work(struct bpf_mem_cache *c)
>  
>  static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
>  {
> -	/* To avoid consuming memory assume that 1st run of bpf
> -	 * prog won't be doing more than 4 map_update_elem from
> -	 * irq disabled region
> +	int cnt = 1;
> +
> +	/* To avoid consuming memory, for non-percpu allocation, assume that
> +	 * 1st run of bpf prog won't be doing more than 4 map_update_elem from
> +	 * irq disabled region if unit size is less than or equal to 256.
> +	 * For all other cases, let us just do one allocation.
>  	 */
> -	alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu), false);
> +	if (!c->percpu_size && c->unit_size <= 256)
> +		cnt = 4;
> +	alloc_bulk(c, cnt, cpu_to_node(cpu), false);
>  }

Another thought about this patch. When the prefilled element is
allocated by the invocation of bpf_percpu_obj_new(), the prefill will
trigger again and this time it will allocate c->batch elements. For
256-bytes unit_size, c->batch will be 64, so the maximal memory
consumption under 128-cpus host will be: 64 * 256 * 128 * 128 = 256MB
when there is one allocation of bpf_percpu_obj_new() on each CPU. And my
question is that should we adjust the low_watermark and high_watermark
accordingly for per-cpu allocation to reduce the memory consumption ?
>  
>  static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)

Re: [PATCH bpf-next v4 3/7] bpf: Allow per unit prefill for non-fix-size percpu memory allocator

[Alexei Starovoitov]

On Sun, Dec 17, 2023 at 10:30:47PM -0800, Yonghong Song wrote:
> @@ -2963,7 +2963,9 @@ static int __init bpf_global_ma_init(void)
>  
>  	ret = bpf_mem_alloc_init(&bpf_global_ma, 0, false);
>  	bpf_global_ma_set = !ret;
> -	return ret;
> +	ret = bpf_mem_alloc_percpu_init(&bpf_global_percpu_ma);
> +	bpf_global_percpu_ma_set = !ret;
> +	return !bpf_global_ma_set || !bpf_global_percpu_ma_set;
...
> -				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
> -					if (!bpf_global_percpu_ma_set) {
> -						mutex_lock(&bpf_percpu_ma_lock);
> -						if (!bpf_global_percpu_ma_set) {
> -							err = bpf_mem_alloc_init(&bpf_global_percpu_ma, 0, true);
> -							if (!err)
> -								bpf_global_percpu_ma_set = true;
> -						}
> -						mutex_unlock(&bpf_percpu_ma_lock);
> -						if (err)
> -							return err;
> -					}
> -				}
> -
>  				if (((u64)(u32)meta.arg_constant.value) != meta.arg_constant.value) {
>  					verbose(env, "local type ID argument must be in range [0, U32_MAX]\n");
>  					return -EINVAL;
> @@ -12096,6 +12079,17 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>  					return -EINVAL;
>  				}
>  
> +				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
> +					if (!bpf_global_percpu_ma_set)
> +						return -ENOMEM;

The patch set looks great except I don't understand this part of the patch
that goes back to allocating bpf_global_percpu_ma by default.
Why allocate even small amount if no bpf prog will use it?
It seems delaying allocation until the verifier sees the need is better.
The rest of the series makes sense.

Re: [PATCH bpf-next v4 3/7] bpf: Allow per unit prefill for non-fix-size percpu memory allocator

[Yonghong Song]

On 12/19/23 8:37 PM, Alexei Starovoitov wrote:
> On Sun, Dec 17, 2023 at 10:30:47PM -0800, Yonghong Song wrote:
>> @@ -2963,7 +2963,9 @@ static int __init bpf_global_ma_init(void)
>>   
>>   	ret = bpf_mem_alloc_init(&bpf_global_ma, 0, false);
>>   	bpf_global_ma_set = !ret;
>> -	return ret;
>> +	ret = bpf_mem_alloc_percpu_init(&bpf_global_percpu_ma);
>> +	bpf_global_percpu_ma_set = !ret;
>> +	return !bpf_global_ma_set || !bpf_global_percpu_ma_set;
> ...
>> -				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
>> -					if (!bpf_global_percpu_ma_set) {
>> -						mutex_lock(&bpf_percpu_ma_lock);
>> -						if (!bpf_global_percpu_ma_set) {
>> -							err = bpf_mem_alloc_init(&bpf_global_percpu_ma, 0, true);
>> -							if (!err)
>> -								bpf_global_percpu_ma_set = true;
>> -						}
>> -						mutex_unlock(&bpf_percpu_ma_lock);
>> -						if (err)
>> -							return err;
>> -					}
>> -				}
>> -
>>   				if (((u64)(u32)meta.arg_constant.value) != meta.arg_constant.value) {
>>   					verbose(env, "local type ID argument must be in range [0, U32_MAX]\n");
>>   					return -EINVAL;
>> @@ -12096,6 +12079,17 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>>   					return -EINVAL;
>>   				}
>>   
>> +				if (meta.func_id == special_kfunc_list[KF_bpf_percpu_obj_new_impl]) {
>> +					if (!bpf_global_percpu_ma_set)
>> +						return -ENOMEM;
> The patch set looks great except I don't understand this part of the patch
> that goes back to allocating bpf_global_percpu_ma by default.
> Why allocate even small amount if no bpf prog will use it?
> It seems delaying allocation until the verifier sees the need is better.
> The rest of the series makes sense.

Thanks for suggestion. Will move early bpf_global_percpu_ma initialization
from __init stage to verifier then. This way, we have zero memory consumption
if bpf_global_percpu_ma is not used.

Re: [PATCH bpf-next v4 4/7] bpf: Refill only one percpu element in memalloc

[Yonghong Song]

On 12/19/23 3:31 AM, Hou Tao wrote:
> Hi,
>
> On 12/18/2023 2:30 PM, Yonghong Song wrote:
>> Typically for percpu map element or data structure, once allocated,
>> most operations are lookup or in-place update. Deletion are really
>> rare. Currently, for percpu data strcture, 4 elements will be
>> refilled if the size is <= 256. Let us just do with one element
>> for percpu data. For example, for size 256 and 128 cpus, the
>> potential saving will be 3 * 256 * 128 * 128 = 12MB.
>>
>> Acked-by: Hou Tao <houtao1@huawei.com>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>>   kernel/bpf/memalloc.c | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
>> index 50ab2fecc005..f37998662146 100644
>> --- a/kernel/bpf/memalloc.c
>> +++ b/kernel/bpf/memalloc.c
>> @@ -485,11 +485,16 @@ static void init_refill_work(struct bpf_mem_cache *c)
>>   
>>   static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
>>   {
>> -	/* To avoid consuming memory assume that 1st run of bpf
>> -	 * prog won't be doing more than 4 map_update_elem from
>> -	 * irq disabled region
>> +	int cnt = 1;
>> +
>> +	/* To avoid consuming memory, for non-percpu allocation, assume that
>> +	 * 1st run of bpf prog won't be doing more than 4 map_update_elem from
>> +	 * irq disabled region if unit size is less than or equal to 256.
>> +	 * For all other cases, let us just do one allocation.
>>   	 */
>> -	alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu), false);
>> +	if (!c->percpu_size && c->unit_size <= 256)
>> +		cnt = 4;
>> +	alloc_bulk(c, cnt, cpu_to_node(cpu), false);
>>   }
> Another thought about this patch. When the prefilled element is
> allocated by the invocation of bpf_percpu_obj_new(), the prefill will
> trigger again and this time it will allocate c->batch elements. For
> 256-bytes unit_size, c->batch will be 64, so the maximal memory
> consumption under 128-cpus host will be: 64 * 256 * 128 * 128 = 256MB

Actually, it should be 48 * 256 * 128 * 128 in the worst case, due to
   c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);

But in reality, for percpu allocation, we probably won't have allocation
for all 128 cpus.

But your point is taken, for percpu allocation, we will have much less
allocations, so we should not use current lower_watermark/upper_watermark used
for non-percpu allocations. So for percpu allocation, I suggest to do
   lower_watermark = 1;
   upper_watermark = 3;
   c->batch = 1;

Thanks!

> when there is one allocation of bpf_percpu_obj_new() on each CPU. And my
> question is that should we adjust the low_watermark and high_watermark
> accordingly for per-cpu allocation to reduce the memory consumption ?
>>   
>>   static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)