From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 7BF231E47CC; Wed, 16 Sep 2026 03:47:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789530432; cv=none; b=Na/YloEBGHE42CJN8R4TtD2DHk11FhuXUALogHWFCVgV3nbUZvOTpkFQU4xJ7LP6HuNFRlgelMztn/qDkm4d5LPXiqi0oHDGfUlmT2VZXn8r/fBNfGktoP3Dgb/iSE8VPd4cKGcJi3dYgjxzrzFqXnClTYhMnZfm4G4wp6Q4vUQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789530432; c=relaxed/simple; bh=gOP7mzIR6JicHMR6kpk3glCyrPVAZFRo2ZW+FrgmoTc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ayEufar5PpzAVVg9p5Xw/da3RAdF4VAOPQhukW9phr6rgJACwSWt3EU/WldIna75MuHoiIDlamoEzKnb3oxktOGZnzrpRXsb5e1LdTQ+HmjLnDcUrUxWm8qdcsxit5Tdq3G4Mu4kWxJf5FYur0ofIhWkLh4Cf5l1HpSuz5BEP0w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=tnJJ08F2; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="tnJJ08F2" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D8ADC1516; Tue, 15 Sep 2026 20:47:04 -0700 (PDT) Received: from e129823.arm.com (e129823.arm.com [10.2.213.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D860B3F882; Tue, 15 Sep 2026 20:47:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1789530428; bh=gOP7mzIR6JicHMR6kpk3glCyrPVAZFRo2ZW+FrgmoTc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tnJJ08F2B08v+fsmMrIYOk0W1spMzOSuvw85ZIxDRL/cerfM015Dh3CGI9V7nyzyf pN74mS7hOpVty/3zNCtYAkuo4HA6jeKDhcnCFOMGC7vZcmFtYKiYsulg+fFme8yPHo CeN5iGihTx4JeaKQbPMyN1tnhGhFIBW2U9blnLao= Date: Wed, 16 Sep 2026 04:47:03 +0100 From: Yeoreum Yun To: Baolin Wang Cc: Yeoreum Yun , Zi Yan , "Liam R. 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 2/2] kselftest: mm: fix intermittent failure khugepaged test Message-ID: References: <20260915-fix_khugepagd_fail-v1-0-bb6f04c8759f@arm.com> <20260915-fix_khugepagd_fail-v1-2-bb6f04c8759f@arm.com> <24690e82-3aab-4f2d-95a7-3bba332ca5bc@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <24690e82-3aab-4f2d-95a7-3bba332ca5bc@linux.alibaba.com> > > > 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"). But, after the thp_enabled changed the THP_MADVISE and then fault, there is the chance to be collpased for anon. I overlook the shmem case. but simple could we do like: diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c index c32244b565658..047524f001532 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)) + madvise(p, len, MADV_NOHUGEPAGE); + return timeout == -1; } > > > + > > 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. What a stupid of me and I post wrong one... thie should be thp_enabled... Apologise :( > > > + > > 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. Sorry this should be thp_enabled... > > > + > > 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); > > > Thanks! -- Sincerely, Yeoreum Yun