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authorDev Jain2024-05-21 13:13:58 +0530
committerAndrew Morton2024-05-24 11:55:06 -0700
commitfb9293b6b0156fbf6ab97a1625d99a29c36d9f0c (patch)
tree35985ca33b5da56db6dfe76ca88f1b8cab6b34fd /tools/debugging
parent9ad665ef55eaad1ead1406a58a34f615a7c18b5e (diff)
selftests/mm: compaction_test: fix bogus test success and reduce probability of OOM-killer invocation
Reset nr_hugepages to zero before the start of the test. If a non-zero number of hugepages is already set before the start of the test, the following problems arise: - The probability of the test getting OOM-killed increases. Proof: The test wants to run on 80% of available memory to prevent OOM-killing (see original code comments). Let the value of mem_free at the start of the test, when nr_hugepages = 0, be x. In the other case, when nr_hugepages > 0, let the memory consumed by hugepages be y. In the former case, the test operates on 0.8 * x of memory. In the latter, the test operates on 0.8 * (x - y) of memory, with y already filled, hence, memory consumed is y + 0.8 * (x - y) = 0.8 * x + 0.2 * y > 0.8 * x. Q.E.D - The probability of a bogus test success increases. Proof: Let the memory consumed by hugepages be greater than 25% of x, with x and y defined as above. The definition of compaction_index is c_index = (x - y)/z where z is the memory consumed by hugepages after trying to increase them again. In check_compaction(), we set the number of hugepages to zero, and then increase them back; the probability that they will be set back to consume at least y amount of memory again is very high (since there is not much delay between the two attempts of changing nr_hugepages). Hence, z >= y > (x/4) (by the 25% assumption). Therefore, c_index = (x - y)/z <= (x - y)/y = x/y - 1 < 4 - 1 = 3 hence, c_index can always be forced to be less than 3, thereby the test succeeding always. Q.E.D Link: https://lkml.kernel.org/r/20240521074358.675031-4-dev.jain@arm.com Fixes: bd67d5c15cc1 ("Test compaction of mlocked memory") Signed-off-by: Dev Jain <dev.jain@arm.com> Cc: <stable@vger.kernel.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Sri Jayaramappa <sjayaram@akamai.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'tools/debugging')
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