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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 Cc: Andrew Morton , David Hildenbrand , Shuah Khan References: <20260921-fix_khugepagd_fail-v2-0-3c2877beef61@arm.com> <20260921-fix_khugepagd_fail-v2-2-3c2877beef61@arm.com> From: Baolin Wang In-Reply-To: <20260921-fix_khugepagd_fail-v2-2-3c2877beef61@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 8wsnmnk4nnafwwqwicp6u1px7map68wn X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A34D740004 X-HE-Tag: 1790134120-740114 X-HE-Meta: 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 V3++RUJQ Ft4bUuSCz7HQZR7KDFoms5gCHq26hb+53prqELx+7rhYWan4jRkL3S1qGIchCgvxct7PJIffPnThRGLnrq4L/LQdHocogBhqt5GHFoz7+IfcZ10TAdfUZgBRQ4Ly5YoQn7DxKS78ebcVSyGZyNZpyMcHn++DSkntrTJeRYl5bAISi+DuxFUNUEBs1LvD5RLwvYQGBHr7sxU59eT287m7j7lY8KnpzlYDec8IXPnoCMK58VyKgUKb7zIYsWpsDm+HLlIf0QF8CQhUZwqFfO10nK/9j5kDb1drKhCT3aTkhFqAVNPC+UUcTjq7ycpasyyupZd8XMqW7b6fjFGA+jQUp55u8I6jAOMFvkcuZBwPng71llho= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 > + madvise(p, len, MADV_NOHUGEPAGE); > + > return timeout == -1; > } > >