We recently encountered a bug that makes all zswap store attempt fail.
Specifically, after:
"141fdeececb3 mm/zswap: delay the initialization of zswap"
if we build a kernel with zswap disabled by default, then enabled after
the swapfile is set up, the zswap tree will not be initialized. As a
result, all zswap store calls will be short-circuited. We have to
perform another swapon to get zswap working properly again.
Fortunately, this issue has since been fixed by the patch that kills
frontswap:
"42c06a0e8ebe mm: kill frontswap"
which performs zswap_swapon() unconditionally, i.e always initializing
the zswap tree.
This test add a sanity check that ensure zswap storing works as
intended.
Signed-off-by: Nhat Pham <[email protected]>
---
tools/testing/selftests/cgroup/test_zswap.c | 48 +++++++++++++++++++++
1 file changed, 48 insertions(+)
diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 49def87a909b..c99d2adaca3f 100644
--- a/tools/testing/selftests/cgroup/test_zswap.c
+++ b/tools/testing/selftests/cgroup/test_zswap.c
@@ -55,6 +55,11 @@ static int get_zswap_written_back_pages(size_t *value)
return read_int("/sys/kernel/debug/zswap/written_back_pages", value);
}
+static long get_zswpout(const char *cgroup)
+{
+ return cg_read_key_long(cgroup, "memory.stat", "zswpout ");
+}
+
static int allocate_bytes(const char *cgroup, void *arg)
{
size_t size = (size_t)arg;
@@ -68,6 +73,48 @@ static int allocate_bytes(const char *cgroup, void *arg)
return 0;
}
+/*
+ * Sanity test to check that pages are written into zswap.
+ */
+static int test_zswap_usage(const char *root)
+{
+ long zswpout_before, zswpout_after;
+ int ret = KSFT_FAIL;
+ char *test_group;
+
+ /* Set up */
+ test_group = cg_name(root, "no_shrink_test");
+ if (!test_group)
+ goto out;
+ if (cg_create(test_group))
+ goto out;
+ if (cg_write(test_group, "memory.max", "1M"))
+ goto out;
+
+ zswpout_before = get_zswpout(test_group);
+ if (zswpout_before < 0) {
+ ksft_print_msg("Failed to get zswpout\n");
+ goto out;
+ }
+
+ /* Allocate more than memory.max to push memory into zswap */
+ if (cg_run(test_group, allocate_bytes, (void *)MB(4)))
+ goto out;
+
+ /* Verify that pages come into zswap */
+ zswpout_after = get_zswpout(test_group);
+ if (zswpout_after <= zswpout_before) {
+ ksft_print_msg("zswpout does not increase after test program\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 not be triggered.
@@ -235,6 +282,7 @@ struct zswap_test {
int (*fn)(const char *root);
const char *name;
} tests[] = {
+ T(test_zswap_usage),
T(test_no_kmem_bypass),
T(test_no_invasive_cgroup_shrink),
};
--
2.34.1
On Fri, 2023-10-20 at 15:20 -0700, Nhat Pham wrote:
>
> This test add a sanity check that ensure zswap storing works as
> intended.
>
> Signed-off-by: Nhat Pham <[email protected]>
>
Acked-by: Rik van Riel <[email protected]>
--
All Rights Reversed.