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[v1,0/2] selftests: mm: cow: flag vmsplice() hugetlb tests as XFAIL

Message ID 20240502085259.103784-1-david@redhat.com
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Series selftests: mm: cow: flag vmsplice() hugetlb tests as XFAIL | expand

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David Hildenbrand May 2, 2024, 8:52 a.m. UTC 
The failing hugetlb vmsplice() COW tests keep confusing people, and
having tests that have been failing for years and likely will keep failing
for years to come because nobody cares enough is rather suboptimal. Let's
mark them as XFAIL and document why fixing them is not that easy as
it would appear at first sight.

More details can be found in [1], especially around how hugetlb pages
cannot really be overcommitted, and why we don't particularly care about
these vmsplice() leaks for hugetlb -- in contrast to ordinary memory.

[1] https://lore.kernel.org/all/8b42a24d-caf0-46ef-9e15-0f88d47d2f21@redhat.com/

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Shuah Khan <shuah@kernel.org>

David Hildenbrand (2):
  selftests: mm: cow: flag vmsplice() hugetlb tests as XFAIL
  mm/hugetlb: document why hugetlb uses folio_mapcount() for COW reuse
    decisions

 mm/hugetlb.c                     |   7 ++
 tools/testing/selftests/mm/cow.c | 106 +++++++++++++++++++++----------
 2 files changed, 78 insertions(+), 35 deletions(-)