From: Andrew Morton <akpm@linux-foundation.org>
To: Yeoreum Yun <yeoreum.yun@arm.com>
Cc: Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
"Liam R. Howlett" <liam@infradead.org>,
Nico Pache <nico.pache@linux.dev>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>, Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Kiryl Shutsemau <kas@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>,
linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org,
David Hildenbrand <david@kernel.org>,
Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH 0/2] kselftest: mm: fix intermittent failure khugepaged test
Date: Tue, 15 Sep 2026 18:15:19 -0700 [thread overview]
Message-ID: <20260915181519.648c2962143b761cf02efd17@linux-foundation.org> (raw)
In-Reply-To: <20260915-fix_khugepagd_fail-v1-0-bb6f04c8759f@arm.com>
On Tue, 15 Sep 2026 10:21:35 +0100 Yeoreum Yun <yeoreum.yun@arm.com> wrote:
> There are intermittent failures in collapse_max_ptes_swap() and
> collapse_max_ptes_shared() when using the khugepaged_context:
>
> # Run test: collapse_max_ptes_shared (khugepaged:anon)
> # Allocate huge page... OK
> # Share huge page over fork()... OK
> # Trigger CoW on page 1023 of 2048... OK
> # Maybe collapse with max_ptes_shared exceeded.... OK
> # Trigger CoW on page 1024 of 2048... Fail
> Bail out! Unexpected huge page
> # Planned tests != run tests (26 != 23)
> # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0
>
> # Run test: collapse_max_ptes_swap (khugepaged:anon)
> # Swapout 257 of 2048 pages... OK
> # Maybe collapse with max_ptes_swap exceeded.... OK
> # Swapout 256 of 2048 pages... OK
> Bail out! Unexpected huge page
> # Planned tests != run tests (26 != 17)
> # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0
>
> This happens because khugepaged may collapse the pages before wait_for_scan()
> is called, causing a sanity check that expects uncollapsed pages to fail.
Is this something we should be testing for? If I'm understanding
correctly, success/failure is dependent on timing vargaries inside the
kernel and that isn't something we can reliably test for.
IOW, should we say "bad idea" and just delete this test case?
next prev parent reply other threads:[~2026-09-16 1:15 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-15 9:21 Yeoreum Yun
2026-09-15 9:21 ` [PATCH 1/2] kselftest: mm: return fail when child test result is fail in khugepaged Yeoreum Yun
2026-09-15 9:21 ` [PATCH 2/2] kselftest: mm: fix intermittent failure khugepaged test Yeoreum Yun
2026-09-16 2:56 ` Baolin Wang
2026-09-16 3:47 ` Yeoreum Yun
2026-09-16 1:15 ` Andrew Morton [this message]
2026-09-16 2:21 ` [PATCH 0/2] " Yeoreum Yun
2026-09-16 6:41 ` David Hildenbrand (Arm)
2026-09-16 7:06 ` Yeoreum Yun
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