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The test_memcg_protection() function is used for the test_memcg_min and
test_memcg_low sub-tests. This function generates a set of parent/child
cgroups like:
parent: memory.min/low = 50M
child 0: memory.min/low = 75M, memory.current = 50M
child 1: memory.min/low = 25M, memory.current = 50M
child 2: memory.min/low = 0, memory.current = 50M
After applying memory pressure, the function expects the following actual
memory usages.
parent: memory.current ~= 50M
child 0: memory.current ~= 29M
child 1: memory.current ~= 21M
child 2: memory.current ~= 0
In reality, the actual memory usages can differ quite a bit from the
expected values. It uses an error tolerance of 10% with the
values_close() helper.
Both the test_memcg_min and test_memcg_low sub-tests can fail sporadically
because the actual memory usage exceeds the 10% error tolerance. Below
are a sample of the usage data of the tests runs that fail.
Child Actual usage Expected usage %err
----- ------------ -------------- ----
1 16990208 22020096 -12.9%
1 17252352 22020096 -12.1%
0 37699584 30408704 +10.7%
1 14368768 22020096 -21.0%
1 16871424 22020096 -13.2%
The current 10% error tolerenace might be right at the time
test_memcontrol.c was first introduced in v4.18 kernel, but memory reclaim
have certainly evolved quite a bit since then which may result in a bit
more run-to-run variation than previously expected.
Increase the error tolerance to 15% for child 0 and 20% for child 1 to
minimize the chance of this type of failure. The tolerance is bigger for
child 1 because an upswing in child 0 corresponds to a smaller %err than a
similar downswing in child 1 due to the way %err is used in
values_close().
Before this patch, a 100 test runs of test_memcontrol produced the
following results:
17 not ok 1 test_memcg_min
22 not ok 2 test_memcg_low
After applying this patch, there were no test failure for test_memcg_min
and test_memcg_low in 100 test runs. However, these tests may still fail
once in a while if the memory usage goes beyond the newly extended range.
Link: https://lkml.kernel.org/r/20250502010443.106022-3-longman@redhat.com
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.