Commit 6479b292 authored by Nhat Pham's avatar Nhat Pham Committed by Andrew Morton
Browse files

selftests: add a sanity check for zswap 

We recently encountered a bug that makes all zswap store attempt fail. 
Specifically, after:

"141fdeec 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:

"42c06a0e 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.

Link: https://lkml.kernel.org/r/20231020222009.2358953-1-nphamcs@gmail.com


Signed-off-by: default avatarNhat Pham <nphamcs@gmail.com>
Acked-by: default avatarRik van Riel <riel@surriel.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
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 9e1b016a

tools/testing/selftests/cgroup/test_zswap.c

+48 −0
Original line number Diff line number Diff line
@@ -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),

};