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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , Shuah Khan Subject: Re: [PATCH v2 2/2] kselftest: mm: fix intermittent failure khugepaged test Message-ID: References: <20260921-fix_khugepagd_fail-v2-0-3c2877beef61@arm.com> <20260921-fix_khugepagd_fail-v2-2-3c2877beef61@arm.com> <6cc12fe6-4f2f-47b6-b821-8a507eb80b46@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 2363F120002 X-Rspam-User: X-Stat-Signature: 5cssushuxhasqdg3i9iqrcbectj9dkcm X-HE-Tag: 1790176860-209601 X-HE-Meta: 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 5hCkfdM5 1q+58WirAUboLjOkuMRVA1pv7Dp/y4i4wAfNfJ1MBN0eaRkO48b51Z8oyRqOmOH0BBesXcdYLYnXiAiqLsO8teWm3GObEICg3K62wi6Ny9wYKbGkuujXpr1U7FQsG1hdtnVEXLE4BKyTOHbJiOLOdWWLlFOjxnyLVOn4w1d7kjcTBcARehWiRUmdUSfQyjc7rpl+RH7lxE8hIGZ0R/SOICWqQpzPqiDTvL7qEvxbPJU2ZgwQDzHHMD11RVlSewTJGpFVUU6gPRI6ORlmVosaZpJRcgA3yOW62qfhl3/2x1L8n0rxjPDsKEKoIdDXCrn9rJeRH Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On 9/23/26 12:54, Yeoreum Yun wrote: > >> > >> > >> On 9/21/26 6:35 PM, Yeoreum Yun wrote: > >>> There are intermittent failures in collapse_max_ptes_swap() and > >>> collapse_max_ptes_shared() when using the khugepaged_context: > >>> > >>> // while running ./khugepaged -s 2 > >>> > >>> # 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. > >>> > >>> For example, in collapse_max_ptes_swap(), after faulting the pages back in > >>> and paging out up to max_ptes_swap pages, khugepaged may collapse them again > >>> before c->collapse() is called. > >>> > >>> To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been > >>> collapsed by wait_for_scan() for anon. This prevents khugepaged from > >>> collapsing it again before c->collapse() is called. > >>> > >>> This failure was observed on NVIDIA Spark with 16KB page. > >>> > >>> Signed-off-by: Yeoreum Yun > >>> --- > >>> tools/testing/selftests/mm/khugepaged.c | 3 +++ > >>> 1 file changed, 3 insertions(+) > >>> > >>> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c > >>> index c32244b565658..1aad4bb427ece 100644 > >>> --- a/tools/testing/selftests/mm/khugepaged.c > >>> +++ b/tools/testing/selftests/mm/khugepaged.c > >>> @@ -578,6 +578,9 @@ static bool wait_for_scan(const char *msg, char *p, size_t len, > >>> usleep(TICK); > >>> } > >>> + if (!strncmp(ops->name, "anon", 4)) > >> > >> We usually use the 'if (ops == &__anon_ops)' check in this file to identify > >> anonymous test cases. > >> > >> With that, LGTM. > >> Reviewed-by: Baolin Wang > >> Tested-by: Baolin Wang > > > > I think this is merged at mm/mm-unstable already So, I'll send > > another patch to change it with is_anon(). > > Unless it is in mm-stable we can reasonably squash stuff or resend. This > shouldn't be an independent patch. I see. Thanks! -- Sincerely, Yeoreum Yun