Commit b93c28ff authored by Nhat Pham's avatar Nhat Pham Committed by Andrew Morton
Browse files

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: default avatarNhat Pham <nphamcs@gmail.com>
Suggested-by: default avatarRik van Riel <riel@surriel.com>
Suggested-by: default avatarYosry Ahmed <yosryahmed@google.com>
Acked-by: default avatarYosry 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 012688f6

tools/testing/selftests/cgroup/test_zswap.c

+118 −2
Original line number Diff line number Diff line
@@ -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 @@ 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 < 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),

};