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SubjectRe: [PATCH v4 bpf-next 5/8] bpf: use module_alloc_huge for bpf_prog_pack
On Fri, May 20, 2022 at 04:57:55PM -0700, Song Liu wrote:
> Use module_alloc_huge for bpf_prog_pack so that BPF programs sit on
> PMD_SIZE pages. This benefits system performance by reducing iTLB miss
> rate. Benchmark of a real web service workload shows this change gives
> another ~0.2% performance boost on top of PAGE_SIZE bpf_prog_pack
> (which improve system throughput by ~0.5%).
>
> Also, remove set_vm_flush_reset_perms() from alloc_new_pack() and use
> set_memory_[nx|rw] in bpf_prog_pack_free(). This is because
> VM_FLUSH_RESET_PERMS does not work with huge pages yet. [1]
>
> [1] https://lore.kernel.org/bpf/aeeeaf0b7ec63fdba55d4834d2f524d8bf05b71b.camel@intel.com/
> Suggested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Song Liu <song@kernel.org>
> ---
> kernel/bpf/core.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index cacd8684c3c4..b64d91fcb0ba 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -857,7 +857,7 @@ static size_t select_bpf_prog_pack_size(void)
> void *ptr;
>
> size = BPF_HPAGE_SIZE * num_online_nodes();
> - ptr = module_alloc(size);
> + ptr = module_alloc_huge(size);
>
> /* Test whether we can get huge pages. If not just use PAGE_SIZE
> * packs.
> @@ -881,7 +881,7 @@ static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_ins
> GFP_KERNEL);
> if (!pack)
> return NULL;
> - pack->ptr = module_alloc(bpf_prog_pack_size);
> + pack->ptr = module_alloc_huge(bpf_prog_pack_size);
> if (!pack->ptr) {
> kfree(pack);
> return NULL;
> @@ -890,7 +890,6 @@ static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_ins
> 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;
> @@ -909,10 +908,9 @@ static void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insn
>
> if (size > bpf_prog_pack_size) {
> size = round_up(size, PAGE_SIZE);
> - ptr = module_alloc(size);
> + ptr = module_alloc_huge(size);
> if (ptr) {
> bpf_fill_ill_insns(ptr, size);
> - set_vm_flush_reset_perms(ptr);
> set_memory_ro((unsigned long)ptr, size / PAGE_SIZE);
> set_memory_x((unsigned long)ptr, size / PAGE_SIZE);
> }
> @@ -949,6 +947,8 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
>
> mutex_lock(&pack_mutex);
> if (hdr->size > bpf_prog_pack_size) {
> + set_memory_nx((unsigned long)hdr, hdr->size / PAGE_SIZE);
> + set_memory_rw((unsigned long)hdr, hdr->size / PAGE_SIZE);

set_memory_{nx,rw} can fail. Please take care of error handling.

> module_memfree(hdr);
> goto out;
> }
> @@ -975,6 +975,8 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
> if (bitmap_find_next_zero_area(pack->bitmap, bpf_prog_chunk_count(), 0,
> bpf_prog_chunk_count(), 0) == 0) {
> list_del(&pack->list);
> + set_memory_nx((unsigned long)pack->ptr, bpf_prog_pack_size / PAGE_SIZE);
> + set_memory_rw((unsigned long)pack->ptr, bpf_prog_pack_size / PAGE_SIZE);

ditto.

> module_memfree(pack->ptr);
> kfree(pack);
> }
> --
> 2.30.2
>
>

--
Sincerely yours,
Mike.

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