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 ?
> +
> 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.
> +
> + 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
low_watermark as 0 to prevent potential refill in unit_alloc() if the
initialization of the current unit fails ?
> + 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));
>
.
