The patch titled
Subject: selftests: cgroup: add zswap-memcg unwanted writeback test
has been added to the -mm mm-unstable branch. Its filename is
selftests-cgroup-add-zswap-memcg-unwanted-writeback-test.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-cgroup-add-zswap-memcg-unwanted-writeback-test.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Subject: selftests: cgroup: add zswap-memcg unwanted writeback test
Date: Wed, 21 Jun 2023 17:35:48 +0200
Add a test to verify that when a memcg hits its limit in zswap, it doesn't
trigger an unwanted writeback that would result in pages not owned by that
memcg to be sent to disk, even if zswap isn't full. This was fixed by
commit 0bdf0efa180a("zswap: do not shrink if cgroup may not zswap").
Link: https://lkml.kernel.org/r/20230621153548.428093-4-cerasuolodomenico@xxxxxxxxx
Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Cc: Dan Streetman <ddstreet@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Seth Jennings <sjenning@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/cgroup/test_zswap.c | 61 ++++++++++++++++++
1 file changed, 61 insertions(+)
--- a/tools/testing/selftests/cgroup/test_zswap.c~selftests-cgroup-add-zswap-memcg-unwanted-writeback-test
+++ a/tools/testing/selftests/cgroup/test_zswap.c
@@ -50,6 +50,66 @@ static int get_zswap_stored_pages(size_t
return read_int("/sys/kernel/debug/zswap/stored_pages", value);
}
+static int get_zswap_written_back_pages(size_t *value)
+{
+ return read_int("/sys/kernel/debug/zswap/written_back_pages", value);
+}
+
+static int allocate_bytes(const char *cgroup, void *arg)
+{
+ size_t size = (size_t)arg;
+ char *mem = (char *)malloc(size);
+
+ if (!mem)
+ return -1;
+ for (int i = 0; i < size; i += 4095)
+ mem[i] = 'a';
+ free(mem);
+ return 0;
+}
+
+/*
+ * When trying to store a memcg page in zswap, if the memcg hits its memory
+ * limit in zswap, writeback should not be triggered.
+ *
+ * This was fixed with commit 0bdf0efa180a("zswap: do not shrink if cgroup may
+ * not zswap"). Needs to be revised when a per memcg writeback mechanism is
+ * implemented.
+ */
+static int test_no_invasive_cgroup_shrink(const char *root)
+{
+ size_t written_back_before, written_back_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;
+ if (cg_write(test_group, "memory.zswap.max", "10K"))
+ goto out;
+ if (get_zswap_written_back_pages(&written_back_before))
+ goto out;
+
+ /* Allocate 10x memory.max to push memory into zswap */
+ if (cg_run(test_group, allocate_bytes, (void *)MB(10)))
+ goto out;
+
+ /* Verify that no writeback happened because of the memcg allocation */
+ if (get_zswap_written_back_pages(&written_back_after))
+ goto out;
+ if (written_back_after == written_back_before)
+ ret = KSFT_PASS;
+out:
+ cg_destroy(test_group);
+ free(test_group);
+ return ret;
+}
+
struct no_kmem_bypass_child_args {
size_t target_alloc_bytes;
size_t child_allocated;
@@ -176,6 +236,7 @@ struct zswap_test {
const char *name;
} tests[] = {
T(test_no_kmem_bypass),
+ T(test_no_invasive_cgroup_shrink),
};
#undef T
_
Patches currently in -mm which might be from cerasuolodomenico@xxxxxxxxx are
selftests-cgroup-add-test_zswap-program.patch
selftests-cgroup-add-test_zswap-with-no-kmem-bypass-test.patch
selftests-cgroup-add-zswap-memcg-unwanted-writeback-test.patch
