On Tue, Mar 24, 2020 at 4:31 PM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
>
> For each prog/btf load we allocate and free 16 megs of verifier buffer.
> On production systems it doesn't really make sense because the
> programs/btf have gone through extensive testing and (mostly) guaranteed
> to successfully load.
>
> Let's switch to a much smaller buffer by default (128 bytes, sys_bpf
> doesn't accept smaller log buffer) and resize it if the kernel returns
> ENOSPC. On the first ENOSPC error we resize the buffer to BPF_LOG_BUF_SIZE
> and then, on each subsequent ENOSPC, we keep doubling the buffer.
>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> ---
> tools/lib/bpf/btf.c | 10 +++++++++-
> tools/lib/bpf/libbpf.c | 10 ++++++++--
> tools/lib/bpf/libbpf_internal.h | 2 ++
> 3 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 3d1c25fc97ae..53c7efc3b347 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -657,13 +657,14 @@ int btf__finalize_data(struct bpf_object *obj, struct btf *btf)
>
> int btf__load(struct btf *btf)
> {
> - __u32 log_buf_size = BPF_LOG_BUF_SIZE;
> + __u32 log_buf_size = BPF_MIN_LOG_BUF_SIZE;
> char *log_buf = NULL;
> int err = 0;
>
> if (btf->fd >= 0)
> return -EEXIST;
>
> +retry_load:
> log_buf = malloc(log_buf_size);
> if (!log_buf)
> return -ENOMEM;
I'd argue that on first try we shouldn't allocate log_buf at all, then
start allocating it using reasonable starting size (see below).
> @@ -673,6 +674,13 @@ int btf__load(struct btf *btf)
> btf->fd = bpf_load_btf(btf->data, btf->data_size,
> log_buf, log_buf_size, false);
> if (btf->fd < 0) {
> + if (errno == ENOSPC) {
> + log_buf_size = max((__u32)BPF_LOG_BUF_SIZE,
> + log_buf_size << 1);
> + free(log_buf);
> + goto retry_load;
> + }
> +
> err = -errno;
> pr_warn("Error loading BTF: %s(%d)\n", strerror(errno), errno);
> if (*log_buf)
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 085e41f9b68e..793c81b35ccc 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4855,7 +4855,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
> {
> struct bpf_load_program_attr load_attr;
> char *cp, errmsg[STRERR_BUFSIZE];
> - int log_buf_size = BPF_LOG_BUF_SIZE;
> + size_t log_buf_size = BPF_MIN_LOG_BUF_SIZE;
> char *log_buf;
> int btf_fd, ret;
>
> @@ -4911,7 +4911,13 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
> }
>
> if (errno == ENOSPC) {
same, doing if (!log_buf || errno == ENOSPC) should handle this
without any other major changes?
> - log_buf_size <<= 1;
> + if (errno == ENOSPC) {
> + log_buf_size = max((size_t)BPF_LOG_BUF_SIZE,
> + log_buf_size << 1);
> + free(log_buf);
> + goto retry_load;
> + }
> +
> free(log_buf);
> goto retry_load;
> }
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index 8c3afbd97747..2720f3366798 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -23,6 +23,8 @@
> #define BTF_PARAM_ENC(name, type) (name), (type)
> #define BTF_VAR_SECINFO_ENC(type, offset, size) (type), (offset), (size)
>
> +#define BPF_MIN_LOG_BUF_SIZE 128
This seems way too low, if there is some error it almost certainly
will be too short, probably for few iterations, just causing waste.
Let's make it something a bit more reasonable, like 32KB or something?
> +
> #ifndef min
> # define min(x, y) ((x) < (y) ? (x) : (y))
> #endif
> --
> 2.25.1.696.g5e7596f4ac-goog
>
