On 12/14/23 10:50 PM, Yonghong Song wrote:
On 12/14/23 7:19 PM, Hou Tao wrote:
On 12/15/2023 8:12 AM, 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.
SNIP
index bb1223b21308..43e635c67150 100644
--- a/include/linux/bpf_mem_alloc.h
+++ b/include/linux/bpf_mem_alloc.h
@@ -21,8 +21,15 @@ 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 c34513d645c4..4a9177770f93 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
*
@@ -2938,7 +2938,9 @@ 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 472158f1fb08..aea4cd07c7b6 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 u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256,
512, 1024, 2048, 4096};
Is it better to make it being const ?
Right. We can make it as const.
+
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 *);
@@ -625,6 +629,68 @@ static void bpf_mem_alloc_destroy_cache(struct
bpf_mem_cache *c)
drain_mem_cache(c);
}
+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 | __GFP_ZERO);
+ if (!pcc)
+ return -ENOMEM;
__GFP_ZERO is not needed. __alloc_percpu_gfp() will zero the returned
area by default.
Thanks. Checked the comments in __alloc_percpu_gfp() and indeed, the
returned
buffer has been zeroed.
+
+ ma->caches = pcc;
+ ma->percpu = true;
+ return 0;
+}
+
+int bpf_mem_alloc_percpu_unit_init(struct bpf_mem_alloc *ma, int size)
+{
+ 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 obj_cgroup *objcg = NULL;
+ struct bpf_mem_cache *c;
+
+ /* room for llist_node and per-cpu pointer */
+ percpu_size = LLIST_NODE_SZ + sizeof(void *);
+
+ i = bpf_mem_cache_idx(size);
+ if (i < 0)
+ return -EINVAL;
+
+ err = 0;
+ pcc = ma->caches;
+ unit_size = sizes[i];
+
+#ifdef CONFIG_MEMCG_KMEM
+ objcg = get_obj_cgroup_from_current();
+#endif
+ for_each_possible_cpu(cpu) {
+ cc = per_cpu_ptr(pcc, cpu);
+ c = &cc->cache[i];
+ if (cpu == 0 && c->unit_size)
+ goto out;
+
+ 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);
+
+ if (cpu == 0) {
+ err = check_obj_size(c, i);
+ if (err) {
+ bpf_mem_alloc_destroy_cache(c);
It seems drain_mem_cache() will be enough. Have you considered setting
At prefill stage, looks like the following is enough:
free_all(__llist_del_all(&c->free_llist), percpu);
But I agree that drain_mem_cache() is simpler and is
easier for future potential code change.
low_watermark as 0 to prevent potential refill in unit_alloc() if the
initialization of the current unit fails ?
I think it does make sense. For non-fix-size non-percpu prefill,
if check_obj_size() failed, the prefill will fail, which include
all buckets.
In this case, if it fails for a particular bucket, we should
make sure that bucket always return NULL ptr, so setting the
low_watermark to 0 does make sense.
Thinking again. If the initialization of the current unit
failed, the verification will fail and the corresponding
bpf program will not be able to do memory alloc, so we
should be fine.
But it is totally possible that some prog later may
call bpf_mem_alloc_percpu_unit_init() again with the
same size/bucket. So we should simply reset bpf_mem_cache
to 0 during the previous failed bpf_mem_alloc_percpu_unit_init()
call. Is it possible that check_obj_size() may initially
returns an error but sometime later something in
the kernel changed and the check_obj_size() with the
same size could return true?
+ goto out;
+ }
+ }
+ }
+
+out:
+ return err;
+}
+
static void check_mem_cache(struct bpf_mem_cache *c)
{
WARN_ON_ONCE(!llist_empty(&c->free_by_rcu_ttrace));
.
