Re: [PATCH bpf-next v2 4/4] selftests/bpf: Add tests for memory usage for arena

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Fri Jul 17, 2026 at 7:37 AM EDT, Jiayuan Chen wrote:
> Allocate and free arena pages, both from BPF and via user-space fault-in,
> and check that the map's memlock in fdinfo tracks the number of pages that
> are actually populated.
>
> Like the other arena tests it runs serially.
>
> test:
>   ./test_progs -a arena_mem_usage
>   #5       arena_mem_usage:OK
>   Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

The Sashiko nit is worth addressing, but overall looks fine.

> ---
>  .../bpf/prog_tests/arena_mem_usage.c          | 122 ++++++++++++++++++
>  .../selftests/bpf/progs/arena_mem_usage.c     |  40 ++++++
>  2 files changed, 162 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/arena_mem_usage.c
>  create mode 100644 tools/testing/selftests/bpf/progs/arena_mem_usage.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/arena_mem_usage.c b/tools/testing/selftests/bpf/prog_tests/arena_mem_usage.c
> new file mode 100644
> index 000000000000..14c2d1a1d673
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/arena_mem_usage.c
> @@ -0,0 +1,122 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <test_progs.h>
> +#include <sys/user.h>
> +#ifndef PAGE_SIZE /* on some archs it comes in sys/user.h */
> +#include <unistd.h>
> +#define PAGE_SIZE getpagesize()
> +#endif
> +
> +#include "arena_mem_usage.skel.h"
> +
> +/*
> + * arena_map_mem_usage() is surfaced to user space through the map's
> + * /proc/<pid>/fdinfo/<fd> "memlock:" line (the same value bpftool map show
> + * prints). Read it directly so the test has no external dependency.
> + */
> +static long map_memlock(int map_fd)
> +{
> +	char path[64], line[128];
> +	long memlock = -1;
> +	FILE *f;
> +
> +	snprintf(path, sizeof(path), "/proc/self/fdinfo/%d", map_fd);
> +	f = fopen(path, "r");
> +	if (!ASSERT_OK_PTR(f, "open_fdinfo"))
> +		return -1;
> +	while (fgets(line, sizeof(line), f)) {
> +		if (sscanf(line, "memlock:\t%ld", &memlock) == 1)
> +			break;
> +	}
> +	fclose(f);
> +	ASSERT_NEQ(memlock, -1, "parse_memlock");
> +	return memlock;
> +}
> +
> +static int run(struct bpf_program *prog, const char *name)
> +{
> +	LIBBPF_OPTS(bpf_test_run_opts, opts);
> +	int err = bpf_prog_test_run_opts(bpf_program__fd(prog), &opts);
> +
> +	if (!ASSERT_OK(err, name))
> +		return -1;
> +	if (!ASSERT_OK(opts.retval, name))
> +		return -1;
> +	return 0;
> +}
> +
> +void serial_test_arena_mem_usage(void)
> +{
> +	struct arena_mem_usage *skel;
> +	const long ps = PAGE_SIZE;
> +	char *base;
> +	size_t sz;
> +	int fd, i;
> +
> +	skel = arena_mem_usage__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "open_load"))
> +		return;
> +	fd = bpf_map__fd(skel->maps.arena);
> +
> +	/* Fresh arena: no data pages, and the scratch page is not counted. */
> +	ASSERT_EQ(map_memlock(fd), 0, "initial");
> +
> +	/* BPF-side allocation of 17 pages. */
> +	skel->bss->alloc_cnt = 17;
> +	if (run(skel->progs.alloc, "alloc"))
> +		goto out;
> +	/*
> +	 * A NULL ptr means bpf_arena_alloc_pages() itself failed (e.g. the host
> +	 * is under memory pressure), not a miscount -- flag it distinctly so a
> +	 * red CI run is not mistaken for a counting bug.
> +	 */
> +	if (!ASSERT_OK_PTR(skel->bss->ptr, "arena_alloc_pages"))
> +		goto out;
> +	ASSERT_EQ(map_memlock(fd), 17 * ps, "after_alloc");
> +
> +	/* Free a single page (arena_free_pages page_cnt==1 path). */
> +	skel->bss->free_byte_off = 0;
> +	skel->bss->free_cnt = 1;
> +	if (run(skel->progs.free_pages, "free_one"))
> +		goto out;
> +	ASSERT_EQ(map_memlock(fd), 16 * ps, "after_free_one");
> +
> +	/* Free ten pages in one call (bulk path); only the freed pages count. */
> +	skel->bss->free_byte_off = 1 * ps;
> +	skel->bss->free_cnt = 10;
> +	if (run(skel->progs.free_pages, "free_bulk"))
> +		goto out;
> +	ASSERT_EQ(map_memlock(fd), 6 * ps, "after_free_bulk");
> +
> +	/* Free the remaining six -> arena empty again. */
> +	skel->bss->free_byte_off = 11 * ps;
> +	skel->bss->free_cnt = 6;
> +	if (run(skel->progs.free_pages, "free_rest"))
> +		goto out;
> +	ASSERT_EQ(map_memlock(fd), 0, "after_free_rest");
> +
> +	/*
> +	 * User-space fault-in: touching unallocated arena pages allocates them
> +	 * through arena_vm_fault(). libbpf mmap()s the arena at map_extra during
> +	 * load, so bpf_map__initial_value() hands back that base.
> +	 */
> +	base = bpf_map__initial_value(skel->maps.arena, &sz);
> +	if (!ASSERT_OK_PTR(base, "arena_base"))
> +		goto out;
> +	for (i = 0; i < 8; i++)
> +		base[i * ps] = 1;
> +	ASSERT_EQ(map_memlock(fd), 8 * ps, "after_faultin");
> +
> +	/*
> +	 * Free the faulted-in pages from BPF. They are mapped into the user vma
> +	 * (elevated refcount), so this also exercises the zap path.
> +	 */
> +	skel->bss->ptr = base;
> +	skel->bss->free_byte_off = 0;
> +	skel->bss->free_cnt = 8;
> +	if (run(skel->progs.free_pages, "free_faulted"))
> +		goto out;
> +	ASSERT_EQ(map_memlock(fd), 0, "after_free_faulted");
> +out:
> +	arena_mem_usage__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/arena_mem_usage.c b/tools/testing/selftests/bpf/progs/arena_mem_usage.c
> new file mode 100644
> index 000000000000..455ecd669a5a
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/arena_mem_usage.c
> @@ -0,0 +1,40 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <vmlinux.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_arena_common.h"
> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARENA);
> +	__uint(map_flags, BPF_F_MMAPABLE);
> +	__uint(max_entries, 1000); /* number of pages */
> +#ifdef __TARGET_ARCH_arm64
> +	__ulong(map_extra, 0x1ull << 32); /* start of mmap() region */
> +#else
> +	__ulong(map_extra, 0x1ull << 44); /* start of mmap() region */
> +#endif
> +} arena SEC(".maps");
> +
> +void __arena *ptr;
> +int alloc_cnt;		/* in:  pages to allocate */
> +long free_byte_off;	/* in:  byte offset within ptr to start freeing */
> +int free_cnt;		/* in:  pages to free */
> +
> +SEC("syscall")
> +int alloc(void *ctx)
> +{
> +	ptr = bpf_arena_alloc_pages(&arena, NULL, alloc_cnt, NUMA_NO_NODE, 0);
> +	/* Success/failure is checked from user space via skel->bss->ptr. */
> +	return 0;
> +}
> +
> +SEC("syscall")
> +int free_pages(void *ctx)
> +{
> +	if (!ptr)
> +		return 1;
> +	bpf_arena_free_pages(&arena, (char __arena *)ptr + free_byte_off, free_cnt);
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";