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mm: fix khugepaged activation policy

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[ Upstream commit 00f5810420 ]

Since the introduction of mTHP, the docuementation has stated that
khugepaged would be enabled when any mTHP size is enabled, and disabled
when all mTHP sizes are disabled.  There are 2 problems with this; 1.
this is not what was implemented by the code and 2.  this is not the
desirable behavior.

Desirable behavior is for khugepaged to be enabled when any PMD-sized THP
is enabled, anon or file.  (Note that file THP is still controlled by the
top-level control so we must always consider that, as well as the PMD-size
mTHP control for anon).  khugepaged only supports collapsing to PMD-sized
THP so there is no value in enabling it when PMD-sized THP is disabled.
So let's change the code and documentation to reflect this policy.

Further, per-size enabled control modification events were not previously
forwarded to khugepaged to give it an opportunity to start or stop.
Consequently the following was resulting in khugepaged eroneously not
being activated:

  echo never > /sys/kernel/mm/transparent_hugepage/enabled
  echo always > /sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled

[ryan.roberts@arm.com: v3]
  Link: https://lkml.kernel.org/r/20240705102849.2479686-1-ryan.roberts@arm.com
Link: https://lkml.kernel.org/r/20240705102849.2479686-1-ryan.roberts@arm.com
Link: https://lkml.kernel.org/r/20240704091051.2411934-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Fixes: 3485b88390 ("mm: thp: introduce multi-size THP sysfs interface")
Closes: https://lore.kernel.org/linux-mm/7a0bbe69-1e3d-4263-b206-da007791a5c4@redhat.com/
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Ryan Roberts
2024-07-04 10:10:50 +01:00
committed by Greg Kroah-Hartman
parent 82dd589d30
commit cd0e079e27
4 changed files with 38 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
Documentation/admin-guide/mm/transhuge.rst
View File

@ -202,12 +202,11 @@ PMD-mappable transparent hugepage::
cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size
khugepaged will be automatically started when one or more hugepage
sizes are enabled (either by directly setting "always" or "madvise",
or by setting "inherit" while the top-level enabled is set to "always"
or "madvise"), and it'll be automatically shutdown when the last
hugepage size is disabled (either by directly setting "never", or by
setting "inherit" while the top-level enabled is set to "never").
khugepaged will be automatically started when PMD-sized THP is enabled
(either of the per-size anon control or the top-level control are set
to "always" or "madvise"), and it'll be automatically shutdown when
PMD-sized THP is disabled (when both the per-size anon control and the
top-level control are "never")
Khugepaged controls
-------------------