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selftests/bpf: Retry stat generation in cgroup_iter_memcg

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Each cgroup_iter_memcg subtest touches 1024 pages and expects the matching
memcg counter to be non-zero. On a host with many CPUs it reads zero
instead:

  test_anon:FAIL:final anon mapped val: actual 0 <= expected 0

memcg stats are cached per-cpu and only become visible once the periodic
flusher runs (FLUSH_TIME, 2s), or once pending updates cross
MEMCG_CHARGE_BATCH * num_online_cpus(). That threshold is 512 pages at 8
CPUs but 8192 at 128, so a single pass no longer reaches it and
bpf_mem_cgroup_flush_stats() returns without flushing anything.

Retry the stat generation, sleeping in between, so that a flusher cycle is
always covered. Sleep before dropping the mapping, so that a flusher cycle
landing in the sleep observes the mapped state. nr_anon_mapped and
nr_file_mapped are rmap gauges, and unmapping first would post a matching
negative delta for the flusher to aggregate to a net zero.

test_file asserts on both nr_file_pages and nr_file_mapped, which have
different lifetimes, as page cache pages outlive the mapping. Retry
while either one is still zero.

Fixes: 6bce6ddbe6 ("bpf: selftests: selftests for memcg stat kfuncs")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20260814232017.2839959-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2026-08-14 16:20:17 -07:00 committed by Daniel Borkmann
parent 6ab6a94c4f
commit 3d9393ff98
1 changed files with 43 additions and 0 deletions
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43
tools/testing/selftests/bpf/prog_tests/cgroup_iter_memcg.c
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@ -10,6 +10,17 @@
#include "cgroup_iter_memcg.h"
#include "cgroup_iter_memcg.skel.h"
/*
* memcg stats are cached per-cpu and only become visible once the periodic
* flusher runs (FLUSH_TIME, 2s), or once pending updates cross
* MEMCG_CHARGE_BATCH * num_online_cpus(). That threshold grows with the CPU
* count, so on a large machine a single pass does not reach it and
* bpf_mem_cgroup_flush_stats() returns without flushing anything. Retry for
* long enough to cover a flusher cycle.
*/
#define MEMCG_STAT_RETRIES 16
#define MEMCG_STAT_RETRY_DELAY_US (250 * 1000)
static int read_stats(struct bpf_link *link)
{
int fd, ret = 0;
@ -35,11 +46,13 @@ static int read_stats(struct bpf_link *link)
static void test_anon(struct bpf_link *link, struct memcg_query *memcg_query)
{
int retries = 0;
void *map;
size_t len;
len = sysconf(_SC_PAGESIZE) * 1024;
retry:
/*
* Increase memcg anon usage by mapping and writing
* to a new anon region.
@ -53,6 +66,12 @@ static void test_anon(struct bpf_link *link, struct memcg_query *memcg_query)
if (!ASSERT_OK(read_stats(link), "read stats"))
goto cleanup;
if (!memcg_query->nr_anon_mapped && ++retries < MEMCG_STAT_RETRIES) {
usleep(MEMCG_STAT_RETRY_DELAY_US);
munmap(map, len);
goto retry;
}
ASSERT_GT(memcg_query->nr_anon_mapped, 0, "final anon mapped val");
cleanup:
@ -61,6 +80,7 @@ static void test_anon(struct bpf_link *link, struct memcg_query *memcg_query)
static void test_file(struct bpf_link *link, struct memcg_query *memcg_query)
{
int retries = 0;
void *map;
size_t len;
char *path;
@ -76,6 +96,7 @@ static void test_file(struct bpf_link *link, struct memcg_query *memcg_query)
fd = open(path, O_CREAT | O_RDWR, 0644);
if (!ASSERT_OK_FD(fd, "open fd"))
return;
retry:
if (!ASSERT_OK(ftruncate(fd, len), "ftruncate"))
goto cleanup_fd;
@ -88,6 +109,13 @@ static void test_file(struct bpf_link *link, struct memcg_query *memcg_query)
if (!ASSERT_OK(read_stats(link), "read stats"))
goto cleanup_map;
if ((!memcg_query->nr_file_pages || !memcg_query->nr_file_mapped) &&
++retries < MEMCG_STAT_RETRIES) {
usleep(MEMCG_STAT_RETRY_DELAY_US);
munmap(map, len);
goto retry;
}
ASSERT_GT(memcg_query->nr_file_pages, 0, "final file value");
ASSERT_GT(memcg_query->nr_file_mapped, 0, "final file mapped value");
@ -100,6 +128,7 @@ static void test_file(struct bpf_link *link, struct memcg_query *memcg_query)
static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
{
int retries = 0;
size_t len;
int fd;
@ -113,12 +142,18 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
if (!ASSERT_OK_FD(fd, "memfd_create"))
return;
retry:
if (!ASSERT_OK(fallocate(fd, 0, 0, len), "fallocate"))
goto cleanup;
if (!ASSERT_OK(read_stats(link), "read stats"))
goto cleanup;
if (!memcg_query->nr_shmem && ++retries < MEMCG_STAT_RETRIES) {
usleep(MEMCG_STAT_RETRY_DELAY_US);
goto retry;
}
ASSERT_GT(memcg_query->nr_shmem, 0, "final shmem value");
cleanup:
@ -127,11 +162,13 @@ static void test_shmem(struct bpf_link *link, struct memcg_query *memcg_query)
static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
{
int retries = 0;
void *map;
size_t len;
len = sysconf(_SC_PAGESIZE) * 1024;
retry:
/* Create region to use for triggering a page fault. */
map = mmap(NULL, len, PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (!ASSERT_NEQ(map, MAP_FAILED, "mmap anon"))
@ -143,6 +180,12 @@ static void test_pgfault(struct bpf_link *link, struct memcg_query *memcg_query)
if (!ASSERT_OK(read_stats(link), "read stats"))
goto cleanup;
if (!memcg_query->pgfault && ++retries < MEMCG_STAT_RETRIES) {
usleep(MEMCG_STAT_RETRY_DELAY_US);
munmap(map, len);
goto retry;
}
ASSERT_GT(memcg_query->pgfault, 0, "final pgfault val");
cleanup: