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Message-Id: <20240205225608.3083251-4-nphamcs@gmail.com>
Date: Mon, 5 Feb 2024 14:56:08 -0800
From: Nhat Pham <nphamcs@...il.com>
To: akpm@...ux-foundation.org
Cc: riel@...riel.com,
shuah@...nel.org,
hannes@...xchg.org,
yosryahmed@...gle.com,
tj@...nel.org,
lizefan.x@...edance.com,
roman.gushchin@...ux.dev,
linux-mm@...ck.org,
kernel-team@...a.com,
linux-kernel@...r.kernel.org,
cgroups@...r.kernel.org,
linux-kselftest@...r.kernel.org
Subject: [PATCH v3 3/3] selftests: add zswapin and no zswap tests
Add a selftest to cover the zswapin code path, allocating more memory
than the cgroup limit to trigger swapout/zswapout, then reading the
pages back in memory several times. This is inspired by a recently
encountered kernel crash on the zswapin path in our internal kernel,
which went undetected because of a lack of test coverage for this path.
Add a selftest to verify that when memory.zswap.max = 0, no pages can go
to the zswap pool for the cgroup.
Suggested-by: Rik van Riel <riel@...riel.com>
Suggested-by: Yosry Ahmed <yosryahmed@...gle.com>
Signed-off-by: Nhat Pham <nphamcs@...il.com>
---
tools/testing/selftests/cgroup/test_zswap.c | 120 +++++++++++++++++++-
1 file changed, 119 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 32ce975b21d1..c263610a4a60 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -60,6 +60,27 @@ static long get_zswpout(const char *cgroup)
return cg_read_key_long(cgroup, "memory.stat", "zswpout ");
}
+static int allocate_and_read_bytes(const char *cgroup, void *arg)
+{
+ size_t size = (size_t)arg;
+ char *mem = (char *)malloc(size);
+ int ret = 0;
+
+ if (!mem)
+ return -1;
+ for (int i = 0; i < size; i += 4095)
+ mem[i] = 'a';
+
+ /* go through the allocated memory to (z)swap in and out pages */
+ for (int i = 0; i < size; i += 4095) {
+ if (mem[i] != 'a')
+ ret = -1;
+ }
+
+ free(mem);
+ return ret;
+}
+
static int allocate_bytes(const char *cgroup, void *arg)
{
size_t size = (size_t)arg;
@@ -100,7 +121,6 @@ static int test_zswap_usage(const char *root)
int ret = KSFT_FAIL;
char *test_group;
- /* Set up */
test_group = cg_name(root, "no_shrink_test");
if (!test_group)
goto out;
@@ -133,6 +153,102 @@ static int test_zswap_usage(const char *root)
return ret;
}
+/*
+ * Check that when memory.zswap.max = 0, no pages can go to the zswap pool for
+ * the cgroup.
+ */
+static int test_swapin_nozswap(const char *root)
+{
+ int ret = KSFT_FAIL;
+ char *test_group;
+ long swap_peak, zswpout;
+
+ test_group = cg_name(root, "no_zswap_test");
+ if (!test_group)
+ goto out;
+ if (cg_create(test_group))
+ goto out;
+ if (cg_write(test_group, "memory.max", "8M"))
+ goto out;
+ if (cg_write(test_group, "memory.zswap.max", "0"))
+ goto out;
+
+ /* Allocate and read more than memory.max to trigger swapin */
+ if (cg_run(test_group, allocate_and_read_bytes, (void *)MB(32)))
+ goto out;
+
+ /* Verify that pages are swapped out, but no zswap happened */
+ swap_peak = cg_read_long(test_group, "memory.swap.peak");
+ if (swap_peak < 0) {
+ ksft_print_msg("failed to get cgroup's swap_peak\n");
+ goto out;
+ }
+
+ if (swap_peak == 0) {
+ ksft_print_msg("pages should be swapped out\n");
+ goto out;
+ }
+
+ zswpout = get_zswpout(test_group);
+ if (zswpout < 0) {
+ ksft_print_msg("failed to get zswpout\n");
+ goto out;
+ }
+
+ if (zswpout > 0) {
+ ksft_print_msg("zswapout > 0 when memory.zswap.max = 0\n");
+ goto out;
+ }
+
+ ret = KSFT_PASS;
+
+out:
+ cg_destroy(test_group);
+ free(test_group);
+ return ret;
+}
+
+/* Simple test to verify the (z)swapin code paths */
+static int test_zswapin(const char *root)
+{
+ int ret = KSFT_FAIL;
+ char *test_group;
+ long zswpin;
+
+ /* Set up */
+ test_group = cg_name(root, "zswapin_test");
+ if (!test_group)
+ goto out;
+ if (cg_create(test_group))
+ goto out;
+ if (cg_write(test_group, "memory.max", "8M"))
+ goto out;
+ if (cg_write(test_group, "memory.zswap.max", "max"))
+ goto out;
+
+ /* Allocate and read more than memory.max to trigger (z)swap in */
+ if (cg_run(test_group, allocate_and_read_bytes, (void *)MB(32)))
+ goto out;
+
+ zswpin = cg_read_key_long(test_group, "memory.stat", "zswpin ");
+ if (zswpin < 0) {
+ ksft_print_msg("failed to get zswpin\n");
+ goto out;
+ }
+
+ if (zswpin == 0) {
+ ksft_print_msg("zswpin should not be 0\n");
+ goto out;
+ }
+
+ ret = KSFT_PASS;
+
+out:
+ cg_destroy(test_group);
+ free(test_group);
+ return ret;
+}
+
/*
* When trying to store a memcg page in zswap, if the memcg hits its memory
* limit in zswap, writeback should affect only the zswapped pages of that
@@ -309,6 +425,8 @@ struct zswap_test {
const char *name;
} tests[] = {
T(test_zswap_usage),
+ T(test_swapin_nozswap),
+ T(test_zswapin),
T(test_no_kmem_bypass),
T(test_no_invasive_cgroup_shrink),
};
--
2.39.3
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