[SRU][O/N][PATCH 0/1] Fix LTP hugetlb failure and prevent potential performance degradation

[Koichiro Den]

BugLink: https://bugs.launchpad.net/bugs/2089768

SRU Justification:

[Impact]

Since upstream commit 003af997c8a9 ("hugetlb: force allocating surplus
hugepages on mempolicy allowed nodes"), the LTP hugetlb test case
'hugemmap10' has started failing frequently. In some testing environments,
it fails almost consistently. This occurs because the surplus allocation
behavior was changed, typically leading to allocations being made on the
least numbered possible NUMA node, even when allocation from the NUMA node
on which the current task running is feasible. This not only causes LTP
test failures but also indicates potential performance degradation.

This patch restores the previous behavior while preserving the benefits
introduced by commit 003af997c8a9. It not only reduces LTP test failure
noise but also prevents performance degradations.

[Fix]

The following upstream commit resolves the issue:
https://lore.kernel.org/all/20241204165503.628784-1-koichiro.den@canonical.com
It does not currently meet stable criteria, so it's unlikely that it will
land in upstream stable tree. That is why this SRU patch.

[Test Plan]

Run the LTP hugemmap10 and verify that it passes consistently on machines
where it previously failed. If such machines are not available, compare
behavior with and without the patch by performing the following steps:
1. prepare a machine which has two or more NUMA nodes, each having usable
   memory
2. run hugemmap10 with naively pinning it onto some CPU of NUMA node #1;
   $ sudo taskset -c {some-cpu-on-node-1} ./hugemmap10
Without this patch, you will observe consistent failures, while with this
patch, the issue will disappear.

[Where problems could occur]

This change affects only hugetlb. If any regressions are found, they would
likely impact hugetlb users.


Koichiro Den (1):
  hugetlb: prioritize surplus allocation from current node

 mm/hugetlb.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

-- 
2.43.0