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Message-ID: <20260206072220.144008-3-jiayuan.chen@linux.dev>
Date: Fri, 6 Feb 2026 15:22:16 +0800
From: Jiayuan Chen <jiayuan.chen@...ux.dev>
To: linux-mm@...ck.org
Cc: Jiayuan Chen <jiayuan.chen@...pee.com>,
Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>,
Michal Koutný <mkoutny@...e.com>,
Jonathan Corbet <corbet@....net>,
Michal Hocko <mhocko@...nel.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Shakeel Butt <shakeel.butt@...ux.dev>,
Muchun Song <muchun.song@...ux.dev>,
Andrew Morton <akpm@...ux-foundation.org>,
Yosry Ahmed <yosry.ahmed@...ux.dev>,
Nhat Pham <nphamcs@...il.com>,
Chengming Zhou <chengming.zhou@...ux.dev>,
Shuah Khan <shuah@...nel.org>,
cgroups@...r.kernel.org,
linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH v2 2/2] selftests/cgroup: add test for zswap incompressible pages
From: Jiayuan Chen <jiayuan.chen@...pee.com>
Add test_zswap_incompressible() to verify that the zswap_incomp memcg
stat correctly tracks incompressible pages.
The test allocates memory filled with random data from /dev/urandom,
which cannot be effectively compressed by zswap. When this data is
swapped out to zswap, it should be stored as-is and tracked by the
zswap_incomp counter.
The test verifies that:
1. Pages are swapped out to zswap (zswpout increases)
2. Incompressible pages are tracked (zswap_incomp increases)
test:
dd if=/dev/zero of=/swapfile bs=1M count=2048
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile
echo Y > /sys/module/zswap/parameters/enabled
./test_zswap
TAP version 13
1..8
ok 1 test_zswap_usage
ok 2 test_swapin_nozswap
ok 3 test_zswapin
ok 4 test_zswap_writeback_enabled
ok 5 test_zswap_writeback_disabled
ok 6 test_no_kmem_bypass
ok 7 test_no_invasive_cgroup_shrink
ok 8 test_zswap_incompressible
Totals: pass:8 fail:0 xfail:0 xpass:0 skip:0 error:0
Signed-off-by: Jiayuan Chen <jiayuan.chen@...pee.com>
---
tools/testing/selftests/cgroup/test_zswap.c | 96 +++++++++++++++++++++
1 file changed, 96 insertions(+)
diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 64ebc3f3f203..8cb8a131357d 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -5,6 +5,7 @@
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
+#include <fcntl.h>
#include <sys/sysinfo.h>
#include <string.h>
#include <sys/wait.h>
@@ -574,6 +575,100 @@ static int test_no_kmem_bypass(const char *root)
return ret;
}
+static int allocate_random_and_wait(const char *cgroup, void *arg)
+{
+ size_t size = (size_t)arg;
+ char *mem;
+ int fd;
+ ssize_t n;
+
+ mem = malloc(size);
+ if (!mem)
+ return -1;
+
+ /* Fill with random data from /dev/urandom - incompressible */
+ fd = open("/dev/urandom", O_RDONLY);
+ if (fd < 0) {
+ free(mem);
+ return -1;
+ }
+
+ for (size_t i = 0; i < size; ) {
+ n = read(fd, mem + i, size - i);
+ if (n <= 0)
+ break;
+ i += n;
+ }
+ close(fd);
+
+ /* Touch all pages to ensure they're faulted in */
+ for (size_t i = 0; i < size; i += 4096)
+ mem[i] = mem[i];
+
+ /* Keep memory alive for parent to reclaim and check stats */
+ pause();
+ free(mem);
+ return 0;
+}
+
+static long get_zswap_incomp(const char *cgroup)
+{
+ return cg_read_key_long(cgroup, "memory.stat", "zswap_incomp ");
+}
+
+/*
+ * Test that incompressible pages (random data) are tracked by zswap_incomp.
+ *
+ * Since incompressible pages stored in zswap are charged at full PAGE_SIZE
+ * (no memory savings), we cannot rely on memory.max pressure to push them
+ * into zswap. Instead, we allocate random data within memory.max, then use
+ * memory.reclaim to proactively push pages into zswap while checking the stat
+ * before the child exits (zswap_incomp is a gauge that decreases on free).
+ */
+static int test_zswap_incompressible(const char *root)
+{
+ int ret = KSFT_FAIL;
+ char *test_group;
+ long zswap_incomp;
+ pid_t child_pid;
+ int child_status;
+
+ test_group = cg_name(root, "zswap_incompressible_test");
+ if (!test_group)
+ goto out;
+ if (cg_create(test_group))
+ goto out;
+ if (cg_write(test_group, "memory.max", "32M"))
+ goto out;
+
+ child_pid = cg_run_nowait(test_group, allocate_random_and_wait,
+ (void *)MB(4));
+ if (child_pid < 0)
+ goto out;
+
+ /* Wait for child to finish allocating */
+ usleep(500000);
+
+ /* Proactively reclaim to push random pages into zswap */
+ cg_write_numeric(test_group, "memory.reclaim", MB(4));
+
+ zswap_incomp = get_zswap_incomp(test_group);
+ if (zswap_incomp <= 0) {
+ ksft_print_msg("zswap_incomp not increased: %ld\n", zswap_incomp);
+ goto out_kill;
+ }
+
+ ret = KSFT_PASS;
+
+out_kill:
+ kill(child_pid, SIGTERM);
+ waitpid(child_pid, &child_status, 0);
+out:
+ cg_destroy(test_group);
+ free(test_group);
+ return ret;
+}
+
#define T(x) { x, #x }
struct zswap_test {
int (*fn)(const char *root);
@@ -586,6 +681,7 @@ struct zswap_test {
T(test_zswap_writeback_disabled),
T(test_no_kmem_bypass),
T(test_no_invasive_cgroup_shrink),
+ T(test_zswap_incompressible),
};
#undef T
--
2.43.0
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