linux-kernel - [PATCH v1 0/2] selftests: mm: cow: flag vmsplice() hugetlb tests as XFAIL

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Message-ID: <20240502085259.103784-1-david@redhat.com>
Date: Thu,  2 May 2024 10:52:57 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Shuah Khan <shuah@...nel.org>
Subject: [PATCH v1 0/2] selftests: mm: cow: flag vmsplice() hugetlb tests as XFAIL

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@...ux-foundation.org>
Cc: Muchun Song <muchun.song@...ux.dev>
Cc: Shuah Khan <shuah@...nel.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(-)

-- 
2.44.0