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.

[nphamcs@gmail.com: remove redundant comment, add success checks]
Link: https://lkml.kernel.org/r/20240222043132.616320-1-nphamcs@gmail.com
Link: https://lkml.kernel.org/r/20240205225608.3083251-4-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Suggested-by: Rik van Riel <riel@surriel.com>
Suggested-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
index 32ce975b21d1f535db9d179a29e078344b21553f..f0e488ed90d8959dc5edb83da057741ad6608384 100644 (file)
--- 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 +153,101 @@ out:
        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 < MB(24)) {
+               ksft_print_msg("at least 24MB of memory 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;
+
+       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 < MB(24) / PAGE_SIZE) {
+               ksft_print_msg("at least 24MB should be brought back from zswap\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
@@ -144,7 +259,6 @@ static int test_no_invasive_cgroup_shrink(const char *root)
        size_t control_allocation_size = MB(10);
        char *control_allocation, *wb_group = NULL, *control_group = NULL;
 
-       /* Set up */
        wb_group = setup_test_group_1M(root, "per_memcg_wb_test1");
        if (!wb_group)
                return KSFT_FAIL;
@@ -309,6 +423,8 @@ 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),
 };