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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 , David Hildenbrand , 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: <6cc12fe6-4f2f-47b6-b821-8a507eb80b46@linux.alibaba.com> X-Rspam-User: X-Stat-Signature: xsgeit9ogmk3gxib5piq1yb6hwko4kfj X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: F1F5E140003 X-HE-Tag: 1790160897-301577 X-HE-Meta: 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 EwTKGFVS CQCEFLAyLK3crfmwYYrbJlIUrW2C/8+xvdl1qmDMEpibhJrEzuJdyhOxSalLW8CRdu11w74SLCrUYLOfcrQWVTBkZ1ko62+5f+5M4O94JgAeLnLn/PwBmGC+HGnsRNtQGWnNepctiqh+XnbcYPih9YEwFf5IzQFhiOPvCoZui0IWIVZt3Pf9OlACJ1+99o6alavBpfBO1btW2GdsVg7na1zuRqbt45VsQdYaySvFffmYBTK6ufbHS9eVYpVMI2RwlkDEsgeRqleLfXikO90Di5SZQCeYicg3B5nBS0pCK6Kw+ZnkESqUdNZeJ9yQqNX8cSbrj 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 I think this is merged at mm/mm-unstable already So, I'll send another patch to change it with is_anon(). Thanks! -- Sincerely, Yeoreum Yun