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Baolin Wang 7962e05a83 selftests: khugepaged: fix the shmem collapse failure
When running the khugepaged selftest for shmem (./khugepaged all:shmem), I
encountered the following test failures:

: Run test: collapse_full (khugepaged:shmem)
: Collapse multiple fully populated PTE table.... Fail
: ...
: Run test: collapse_single_pte_entry (khugepaged:shmem)
: Collapse PTE table with single PTE entry present.... Fail
: ...
: Run test: collapse_full_of_compound (khugepaged:shmem)
: Allocate huge page... OK
: Split huge page leaving single PTE page table full of compound pages... OK
: Collapse PTE table full of compound pages.... Fail

The reason for the failure is that it will set MADV_NOHUGEPAGE to prevent
khugepaged from continuing to scan shmem VMA after khugepaged finishes
scanning in the wait_for_scan() function.  Moreover, shmem requires a
refault to establish PMD mappings.

However, after commit 2b0f922323 ("mm: don't install PMD mappings when
THPs are disabled by the hw/process/vma"), PMD mappings are prevented if
the VMA is set with MADV_NOHUGEPAGE flag, so shmem cannot establish PMD
mappings during refault.

One way to fix this issue is to move the MADV_NOHUGEPAGE setting after the
shmem refault.  After shmem refault and check huge, the test case will
unmap the shmem immediately.  So it seems unnecessary to set the
MADV_NOHUGEPAGE.

Then we can simply drop the MADV_NOHUGEPAGE setting, and all khugepaged
test cases passed.

Link: https://lkml.kernel.org/r/d8502fc50d0304c2afd27ced062b1d636b7a872e.1749779183.git.baolin.wang@linux.alibaba.com
Fixes: 2b0f922323 ("mm: don't install PMD mappings when THPs are disabled by the hw/process/vma")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Tested-by: Dev Jain <dev.jain@arm.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2025-07-09 22:42:09 -07:00
Documentation Docs/admin-guide/mm/damon: add DAMON_STAT usage document 2025-07-09 22:41:56 -07:00
LICENSES LICENSES: add CC0-1.0 license text 2025-05-21 14:54:17 +02:00
arch mm/pagewalk: split walk_page_range_novma() into kernel/user parts 2025-07-09 22:42:05 -07:00
block bio: use memzero_page() in bio_truncate() 2025-07-09 22:42:08 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: wp512 - Use API partial block handling 2025-06-23 16:56:56 +08:00
drivers null_blk: use memzero_page() 2025-07-09 22:42:08 -07:00
fs ceph: convert ceph_zero_partial_page() to use a folio 2025-07-09 22:42:09 -07:00
include mm: remove zero_user() 2025-07-09 22:42:09 -07:00
init futex: Temporary disable FUTEX_PRIVATE_HASH 2025-07-01 15:02:05 +02:00
io_uring io_uring-6.16-20250630 2025-06-30 16:32:43 -07:00
ipc - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
kernel mm: use folio_expected_ref_count() helper for reference counting 2025-07-09 22:42:08 -07:00
lib alloc_tag: keep codetag iterator active between read() 2025-07-09 22:42:06 -07:00
mm mm: use folio_expected_ref_count() helper for reference counting 2025-07-09 22:42:08 -07:00
net Including fixes from Bluetooth. 2025-07-03 09:18:55 -07:00
rust Driver core fixes for 6.16-rc3 2025-06-18 14:31:16 -07:00
samples - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
scripts alloc_tag: remove empty module tag section 2025-07-09 22:42:03 -07:00
security selinux: change security_compute_sid to return the ssid or tsid on match 2025-06-19 16:13:16 -04:00
sound ALSA: hda/realtek: Fix built-in mic on ASUS VivoBook X507UAR 2025-06-26 08:02:44 +02:00
tools selftests: khugepaged: fix the shmem collapse failure 2025-07-09 22:42:09 -07:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge branch 'kvm-lockdep-common' into HEAD 2025-05-28 06:29:17 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about `clippy::disallowed_macros` configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore Python compiled bytecode 2025-04-24 10:12:46 -06:00
.mailmap 16 hotfixes. 6 are cc:stable and the remainder address post-6.15 issues 2025-06-27 20:34:10 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml rust: add `.rustfmt.toml` 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Add entry for Shannon Nelson 2025-06-21 07:34:28 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS tools/mm: add script to display page state for a given PID and VADDR 2025-07-09 22:41:53 -07:00
Makefile Linux 6.16-rc5 2025-07-06 14:10:26 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README

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.