lkml.org 
[lkml]   [2022]   [Jan]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v7 bpf-next 7/9] bpf: introduce bpf_prog_pack allocator
From
Date
On 1/29/22 12:45 AM, Song Liu wrote:
> Most BPF programs are small, but they consume a page each. For systems
> with busy traffic and many BPF programs, this could add significant
> pressure to instruction TLB.
>
> Introduce bpf_prog_pack allocator to pack multiple BPF programs in a huge
> page. The memory is then allocated in 64 byte chunks.
>
> Memory allocated by bpf_prog_pack allocator is RO protected after initial
> allocation. To write to it, the user (jit engine) need to use text poke
> API.

Did you benchmark the program load times under this API, e.g. how much
overhead is expected for very large programs?

> Signed-off-by: Song Liu <song@kernel.org>
> ---
> kernel/bpf/core.c | 127 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 127 insertions(+)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index dc0142e20c72..25e34caa9a95 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -805,6 +805,133 @@ int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
> return slot;
> }
>
> +/*
> + * BPF program pack allocator.
> + *
> + * Most BPF programs are pretty small. Allocating a hole page for each
> + * program is sometime a waste. Many small bpf program also adds pressure
> + * to instruction TLB. To solve this issue, we introduce a BPF program pack
> + * allocator. The prog_pack allocator uses HPAGE_PMD_SIZE page (2MB on x86)
> + * to host BPF programs.
> + */
> +#define BPF_PROG_PACK_SIZE HPAGE_PMD_SIZE
> +#define BPF_PROG_CHUNK_SHIFT 6
> +#define BPF_PROG_CHUNK_SIZE (1 << BPF_PROG_CHUNK_SHIFT)
> +#define BPF_PROG_CHUNK_MASK (~(BPF_PROG_CHUNK_SIZE - 1))
> +#define BPF_PROG_CHUNK_COUNT (BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE)
> +
> +struct bpf_prog_pack {
> + struct list_head list;
> + void *ptr;
> + unsigned long bitmap[BITS_TO_LONGS(BPF_PROG_CHUNK_COUNT)];
> +};
> +
> +#define BPF_PROG_MAX_PACK_PROG_SIZE HPAGE_PMD_SIZE
> +#define BPF_PROG_SIZE_TO_NBITS(size) (round_up(size, BPF_PROG_CHUNK_SIZE) / BPF_PROG_CHUNK_SIZE)
> +
> +static DEFINE_MUTEX(pack_mutex);
> +static LIST_HEAD(pack_list);
> +
> +static struct bpf_prog_pack *alloc_new_pack(void)
> +{
> + struct bpf_prog_pack *pack;
> +
> + pack = kzalloc(sizeof(*pack), GFP_KERNEL);
> + if (!pack)
> + return NULL;
> + pack->ptr = module_alloc(BPF_PROG_PACK_SIZE);
> + if (!pack->ptr) {
> + kfree(pack);
> + return NULL;
> + }
> + bitmap_zero(pack->bitmap, BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE);
> + list_add_tail(&pack->list, &pack_list);
> +
> + set_vm_flush_reset_perms(pack->ptr);
> + set_memory_ro((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
> + set_memory_x((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
> + return pack;
> +}
> +
> +static void *bpf_prog_pack_alloc(u32 size)
> +{
> + unsigned int nbits = BPF_PROG_SIZE_TO_NBITS(size);
> + struct bpf_prog_pack *pack;
> + unsigned long pos;
> + void *ptr = NULL;
> +
> + if (size > BPF_PROG_MAX_PACK_PROG_SIZE) {
> + size = round_up(size, PAGE_SIZE);
> + ptr = module_alloc(size);
> + if (ptr) {
> + set_vm_flush_reset_perms(ptr);
> + set_memory_ro((unsigned long)ptr, size / PAGE_SIZE);
> + set_memory_x((unsigned long)ptr, size / PAGE_SIZE);
> + }
> + return ptr;
> + }
> + mutex_lock(&pack_mutex);
> + list_for_each_entry(pack, &pack_list, list) {
> + pos = bitmap_find_next_zero_area(pack->bitmap, BPF_PROG_CHUNK_COUNT, 0,
> + nbits, 0);
> + if (pos < BPF_PROG_CHUNK_COUNT)
> + goto found_free_area;
> + }
> +
> + pack = alloc_new_pack();
> + if (!pack)
> + goto out;

Will this effectively disable the JIT for all bpf_prog_pack_alloc requests <=
BPF_PROG_MAX_PACK_PROG_SIZE when vmap_allow_huge is false (e.g. boot param via
nohugevmalloc) ?

> + pos = 0;
> +
> +found_free_area:
> + bitmap_set(pack->bitmap, pos, nbits);
> + ptr = (void *)(pack->ptr) + (pos << BPF_PROG_CHUNK_SHIFT);
> +
> +out:
> + mutex_unlock(&pack_mutex);
> + return ptr;
> +}
> +
> +static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
> +{
> + struct bpf_prog_pack *pack = NULL, *tmp;
> + unsigned int nbits;
> + unsigned long pos;
> + void *pack_ptr;
> +
> + if (hdr->size > BPF_PROG_MAX_PACK_PROG_SIZE) {
> + module_memfree(hdr);
> + return;
> + }
> +
> + pack_ptr = (void *)((unsigned long)hdr & ~(BPF_PROG_PACK_SIZE - 1));
> + mutex_lock(&pack_mutex);
> +
> + list_for_each_entry(tmp, &pack_list, list) {
> + if (tmp->ptr == pack_ptr) {
> + pack = tmp;
> + break;
> + }
> + }
> +
> + if (WARN_ONCE(!pack, "bpf_prog_pack bug\n"))
> + goto out;
> +
> + nbits = BPF_PROG_SIZE_TO_NBITS(hdr->size);
> + pos = ((unsigned long)hdr - (unsigned long)pack_ptr) >> BPF_PROG_CHUNK_SHIFT;
> +
> + bitmap_clear(pack->bitmap, pos, nbits);
> + if (bitmap_find_next_zero_area(pack->bitmap, BPF_PROG_CHUNK_COUNT, 0,
> + BPF_PROG_CHUNK_COUNT, 0) == 0) {
> + list_del(&pack->list);
> + module_memfree(pack->ptr);
> + kfree(pack);
> + }
> +out:
> + mutex_unlock(&pack_mutex);
> +}
> +
> static atomic_long_t bpf_jit_current;
>
> /* Can be overridden by an arch's JIT compiler if it has a custom,
>

\
 
 \ /
  Last update: 2022-02-01 01:06    [W:0.083 / U:0.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site