On 05.07.24 12:28, Ryan Roberts wrote:
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
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Fixes: 3485b88390b0 ("mm: thp: introduce multi-size THP sysfs interface")
Closes: https://lore.kernel.org/linux-mm/7a0bbe69-1e3d-4263-b206-da007791a5c4@xxxxxxxxxx/
Cc: stable@xxxxxxxxxxxxxxx
---
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
