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Dev Jain fb9293b6b0 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: bd67d5c15c ("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>
2024-05-24 11:55:06 -07:00
arch - A series ("kbuild: enable more warnings by default") from Arnd 2024-05-22 18:59:29 -07:00
block Compactifying bdev flags 2024-05-21 13:02:56 -07:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto This push fixes a bug in the new ecc P521 code as well as a buggy 2024-05-20 08:47:54 -07:00
Documentation lib: add version into /proc/allocinfo output 2024-05-24 11:55:05 -07:00
drivers - A series ("kbuild: enable more warnings by default") from Arnd 2024-05-22 18:59:29 -07:00
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include kasan, fortify: properly rename memintrinsics 2024-05-24 11:55:05 -07:00
init Driver core changes for 6.10-rc1 2024-05-22 12:13:40 -07:00
io_uring Assorted commits that had missed the last merge window... 2024-05-21 13:11:44 -07:00
ipc Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
kernel Driver core changes for 6.10-rc1 2024-05-22 12:13:40 -07:00
lib lib: add version into /proc/allocinfo output 2024-05-24 11:55:05 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/huge_memory: don't unpoison huge_zero_folio 2024-05-24 11:55:05 -07:00
net more s390 updates for 6.10 merge window 2024-05-21 12:09:36 -07:00
rust LoongArch changes for v6.10 2024-05-22 09:43:07 -07:00
samples Char/Misc and other driver subsystem changes for 6.10-rc1 2024-05-22 12:26:46 -07:00
scripts - A series ("kbuild: enable more warnings by default") from Arnd 2024-05-22 18:59:29 -07:00
security KEYS: trusted: Do not use WARN when encode fails 2024-05-21 02:35:10 +03:00
sound - Core Frameworks 2024-05-22 10:49:54 -07:00
tools selftests/mm: compaction_test: fix bogus test success and reduce probability of OOM-killer invocation 2024-05-24 11:55:06 -07:00
usr kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
virt The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
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.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
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COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer 2024-03-27 13:41:02 -05:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Char/Misc and other driver subsystem changes for 6.10-rc1 2024-05-22 12:26:46 -07:00
Makefile arch: add ARCH_HAS_KERNEL_FPU_SUPPORT 2024-05-19 14:36:17 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

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.