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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: <20260915-fix_khugepagd_fail-v1-0-bb6f04c8759f@arm.com> <20260915-fix_khugepagd_fail-v1-2-bb6f04c8759f@arm.com> From: Baolin Wang In-Reply-To: <20260915-fix_khugepagd_fail-v1-2-bb6f04c8759f@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: gxckn3sweudag77aoy1yws16iruypsno X-Rspam-User: X-Rspamd-Queue-Id: E7F871C0002 X-Rspamd-Server: rspam03 X-HE-Tag: 1789527404-208107 X-HE-Meta: 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 qsE6Vkrj BS64cUqp+ueZwbFudydecRmVtRiNN41PZ+TXa3uXcVR8KJgsJ5WmysBhNKZwzAmI17Z2eo47JNXraGdDbtG85S3OoIooJnuckXKRYYdSqf7BoSzDGuKZiSMBIqX5vr7LDOQI1NjMKbMv8PDxqRZAG0eUdcTH/H/jkMuz6BY3LWq2t/tNdYQQ1cp3aXygnfq9okL8dLoOTOmToJtOeblGW5UgHLlxdE/SF/iZztwP8qd3ga45NQoYDeDI1WyVWfJYh9VHTbmOxfnus9tHy73bMMoX/rFiC1YWHJqTtlpdple6wAd/FhUwqcFJja2xUCk/EZPJOQCP1YwbJ3Yxa9xAkgUaVRk3lBUB3/866biwuqgH+UufNEgONyHVjmGqKq/lkORi0z86eg+Diz9M+oVkudwNCoabZeJNGNl6D Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/15/26 5:21 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, change the khugepaged setting from ALWAYS to MADVICE for > the affected tests, and mark the VMA with MADV_NOHUGEPAGE after it has been > collapsed by wait_for_scan(). 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 | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c > index c32244b565658..83e9386bbc842 100644 > --- a/tools/testing/selftests/mm/khugepaged.c > +++ b/tools/testing/selftests/mm/khugepaged.c > @@ -578,6 +578,8 @@ static bool wait_for_scan(const char *msg, char *p, size_t len, > usleep(TICK); > } > > + madvise(p, len, MADV_NOHUGEPAGE); This looks incorrect to me and would reintroduce the previous problem. Please see commit 7962e05a835f ("selftests: khugepaged: fix the shmem collapse failure"). > + > return timeout == -1; > } > > @@ -839,6 +841,7 @@ static void collapse_swapin_single_pte(struct collapse_context *c, struct mem_op > > static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *ops) > { > + struct thp_settings settings = *thp_current_settings(); > int max_ptes_swap = thp_read_num("khugepaged/max_ptes_swap"); > void *p; > > @@ -860,6 +863,9 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o > validate_memory(p, 0, hpage_pmd_size); > > if (c->enforce_pte_scan_limits) { > + settings.hugepages[collapse_order].enabled = THP_MADVISE; > + thp_push_settings(&settings); I'm not sure why the collapse_order setting needs to be changed here. In your test case, you did not use the '-c' parameter to specify the collapse order. > + > ops->fault(p, 0, hpage_pmd_size); > ksft_print_msg("Swapout %d of %d pages...", max_ptes_swap, > hpage_pmd_nr); > @@ -869,12 +875,15 @@ static void collapse_max_ptes_swap(struct collapse_context *c, struct mem_ops *o > success("OK"); > } else { > fail("Fail"); > + thp_pop_settings(); > goto out; > } > > c->collapse("Collapse with max_ptes_swap pages swapped out", p, > 1, ops, true); > validate_memory(p, 0, hpage_pmd_size); > + > + thp_pop_settings(); > } > out: > ops->cleanup_area(p, hpage_pmd_size); > @@ -1075,6 +1084,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o > > static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops *ops) > { > + struct thp_settings settings = *thp_current_settings(); > int max_ptes_shared = thp_read_num("khugepaged/max_ptes_shared"); > int wstatus; > void *p; > @@ -1100,6 +1110,9 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops > 1, ops, !c->enforce_pte_scan_limits); > > if (c->enforce_pte_scan_limits) { > + settings.hugepages[collapse_order].enabled = THP_MADVISE; > + thp_push_settings(&settings); Ditto. > + > ksft_print_msg("Trigger CoW on page %d of %d...", > hpage_pmd_nr - max_ptes_shared, hpage_pmd_nr); > ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared) * > @@ -1111,6 +1124,8 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops > > c->collapse("Collapse with max_ptes_shared PTEs shared", > p, 1, ops, true); > + > + thp_pop_settings(); > } > > validate_memory(p, 0, hpage_pmd_size); >