The patch titled
Subject: Documentation/cgroup-v2: clarify that zswap.writeback is ignored if zswap is disabled
has been added to the -mm mm-unstable branch. Its filename is
documentation-cgroup-v2-clarify-that-zswapwriteback-is-ignored-if-zswap-is-disabled.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/documentation-cgroup-v2-clarify-that-zswapwriteback-is-ignored-if-zswap-is-disabled.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: Mike Yuan <me@xxxxxxxxxxx>
Subject: Documentation/cgroup-v2: clarify that zswap.writeback is ignored if zswap is disabled
Date: Fri, 23 Aug 2024 16:27:11 +0000
As discussed in [1], zswap-related settings natually lose their effect
when zswap is disabled, specifically zswap.writeback here. Be explicit
about this behavior.
[1] https://lore.kernel.org/linux-kernel/CAKEwX=3DMhbwhh-=3DxxCU-RjMXS_n=3D=
RpV3Gtznb2m_3JgL+jzz++g@xxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20240823162506.12117-3-me@xxxxxxxxxxx
Signed-off-by: Mike Yuan <me@xxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michal Koutný <mkoutny@xxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/cgroup/test_zswap.c | 75 ++++++++++++------
1 file changed, 54 insertions(+), 21 deletions(-)
--- a/tools/testing/selftests/cgroup/test_zswap.c~documentation-cgroup-v2-clarify-that-zswapwriteback-is-ignored-if-zswap-is-disabled
+++ a/tools/testing/selftests/cgroup/test_zswap.c
@@ -263,15 +263,13 @@ out:
static int attempt_writeback(const char *cgroup, void *arg)
{
long pagesize = sysconf(_SC_PAGESIZE);
- char *test_group = arg;
size_t memsize = MB(4);
char buf[pagesize];
long zswap_usage;
- bool wb_enabled;
+ bool wb_enabled = *(bool *) arg;
int ret = -1;
char *mem;
- wb_enabled = cg_read_long(test_group, "memory.zswap.writeback");
mem = (char *)malloc(memsize);
if (!mem)
return ret;
@@ -288,12 +286,12 @@ static int attempt_writeback(const char
memcpy(&mem[i], buf, pagesize);
/* Try and reclaim allocated memory */
- if (cg_write_numeric(test_group, "memory.reclaim", memsize)) {
+ if (cg_write_numeric(cgroup, "memory.reclaim", memsize)) {
ksft_print_msg("Failed to reclaim all of the requested memory\n");
goto out;
}
- zswap_usage = cg_read_long(test_group, "memory.zswap.current");
+ zswap_usage = cg_read_long(cgroup, "memory.zswap.current");
/* zswpin */
for (int i = 0; i < memsize; i += pagesize) {
@@ -303,7 +301,7 @@ static int attempt_writeback(const char
}
}
- if (cg_write_numeric(test_group, "memory.zswap.max", zswap_usage/2))
+ if (cg_write_numeric(cgroup, "memory.zswap.max", zswap_usage/2))
goto out;
/*
@@ -312,7 +310,7 @@ static int attempt_writeback(const char
* If writeback is disabled, memory reclaim will fail as zswap is limited and
* it can't writeback to swap.
*/
- ret = cg_write_numeric(test_group, "memory.reclaim", memsize);
+ ret = cg_write_numeric(cgroup, "memory.reclaim", memsize);
if (!wb_enabled)
ret = (ret == -EAGAIN) ? 0 : -1;
@@ -321,12 +319,41 @@ out:
return ret;
}
+static int test_zswap_writeback_one(const char *cgroup, bool wb)
+{
+ long zswpwb_before, zswpwb_after;
+
+ zswpwb_before = get_cg_wb_count(cgroup);
+ if (zswpwb_before != 0) {
+ ksft_print_msg("zswpwb_before = %ld instead of 0\n", zswpwb_before);
+ return -1;
+ }
+
+ if (cg_run(cgroup, attempt_writeback, (void *) &wb))
+ return -1;
+
+ /* Verify that zswap writeback occurred only if writeback was enabled */
+ zswpwb_after = get_cg_wb_count(cgroup);
+ if (zswpwb_after < 0)
+ return -1;
+
+ if (wb != !!zswpwb_after) {
+ ksft_print_msg("zswpwb_after is %ld while wb is %s",
+ zswpwb_after, wb ? "enabled" : "disabled");
+ return -1;
+ }
+
+ return 0;
+}
+
/* Test to verify the zswap writeback path */
static int test_zswap_writeback(const char *root, bool wb)
{
- long zswpwb_before, zswpwb_after;
int ret = KSFT_FAIL;
- char *test_group;
+ char *test_group, *test_group_child = NULL;
+
+ if (cg_read_strcmp(root, "memory.zswap.writeback", "1"))
+ return KSFT_SKIP;
test_group = cg_name(root, "zswap_writeback_test");
if (!test_group)
@@ -336,29 +363,35 @@ static int test_zswap_writeback(const ch
if (cg_write(test_group, "memory.zswap.writeback", wb ? "1" : "0"))
goto out;
- zswpwb_before = get_cg_wb_count(test_group);
- if (zswpwb_before != 0) {
- ksft_print_msg("zswpwb_before = %ld instead of 0\n", zswpwb_before);
+ if (test_zswap_writeback_one(test_group, wb))
goto out;
- }
- if (cg_run(test_group, attempt_writeback, (void *) test_group))
+ /* Reset memory.zswap.max to max (modified by attempt_writeback), and
+ * set up child cgroup, whose memory.zswap.writeback is hardcoded to 1.
+ * Thus, the parent's setting shall be what's in effect. */
+ if (cg_write(test_group, "memory.zswap.max", "max"))
+ goto out;
+ if (cg_write(test_group, "cgroup.subtree_control", "+memory"))
goto out;
- /* Verify that zswap writeback occurred only if writeback was enabled */
- zswpwb_after = get_cg_wb_count(test_group);
- if (zswpwb_after < 0)
+ test_group_child = cg_name(test_group, "zswap_writeback_test_child");
+ if (!test_group_child)
+ goto out;
+ if (cg_create(test_group_child))
+ goto out;
+ if (cg_write(test_group_child, "memory.zswap.writeback", "1"))
goto out;
- if (wb != !!zswpwb_after) {
- ksft_print_msg("zswpwb_after is %ld while wb is %s",
- zswpwb_after, wb ? "enabled" : "disabled");
+ if (test_zswap_writeback_one(test_group_child, wb))
goto out;
- }
ret = KSFT_PASS;
out:
+ if (test_group_child) {
+ cg_destroy(test_group_child);
+ free(test_group_child);
+ }
cg_destroy(test_group);
free(test_group);
return ret;
_
Patches currently in -mm which might be from me@xxxxxxxxxxx are
mm-memcontrol-respect-zswapwriteback-setting-from-parent-cg-too.patch
documentation-cgroup-v2-clarify-that-zswapwriteback-is-ignored-if-zswap-is-disabled.patch
selftests-test_zswap-add-test-for-hierarchical-zswapwriteback.patch
