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 843A03C09EE; Wed, 16 Sep 2026 07:06:58 +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=1789542421; cv=none; b=SLWmXRgr81C7I2AUYJPSzkGn/TRdFh1UBHt0WzzJ1GQAn3ikUL6zI0zOshNCNGQsLykbfa+347JM8PnRKDteF78HeN3V9PtnBf8Gpp8K91t7Rrk0DOb/431/fm2eTwCZ+hf6cYkukQMCB+AWB+ezlEnxcZhsTlUQVJr9SrGLf40= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789542421; c=relaxed/simple; bh=7j41/pbsi2hh7BzOK/zlBjo5ceENRET+9FnTWgUaeYY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Z+gLqQ4I+8cN9ZKrj4qqcwk0ApmY6lmcZStYVx6ZSW7Nm9pFOAIBS78Qc58JJIM0cHNptQDbfSWlYPLa3ErrY80zcf+rRvQsE/DnG/q7fvakFIM0o3is8XVkHjcHiYFIdyYzq5tGk5H9z/eqwe2gDKI3ZBZJdYeL2oSTCCfEeJo= 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=bU8VbXfk; 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="bU8VbXfk" 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 1E0A0152B; Wed, 16 Sep 2026 00:06:54 -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 995AF3F86F; Wed, 16 Sep 2026 00:06:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1789542417; bh=7j41/pbsi2hh7BzOK/zlBjo5ceENRET+9FnTWgUaeYY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bU8VbXfkKaKwuh6T7BWjvzIFRNk1/Mkj14bNCbgP3EMRPQntwVb6eQyRKr/RtoJHR nZXlP4iJoqERz7vC2vDX7Bun0jQtSF23uJZpSIC4RlnrRLdm33e9UUX8fC63WvUnhI 2Wt5RYyChyWHtUQWRzRHrQCFtqWRQD1Q+BwMeRUM= Date: Wed, 16 Sep 2026 08:06:52 +0100 From: Yeoreum Yun To: "David Hildenbrand (Arm)" Cc: Yeoreum Yun , Zi Yan , Baolin Wang , "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 , Shuah Khan Subject: Re: [PATCH 0/2] kselftest: mm: fix intermittent failure khugepaged test Message-ID: References: <20260915-fix_khugepagd_fail-v1-0-bb6f04c8759f@arm.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: On Wed, Sep 16, 2026 at 08:41:00AM +0200, David Hildenbrand (Arm) wrote: > On 9/15/26 11:21, Yeoreum Yun wrote: > > There are intermittent failures in collapse_max_ptes_swap() and > > collapse_max_ptes_shared() when using the khugepaged_context: > > > > # 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. > > ALWAYS also respects MADV_NOHUGEPAGE, so why is the ALWAYS -> MADVICE (MADVISE) > change required? You're right. this is redundant and it's enough only set the VM_NOHUGEPAGE for anon. I'll remove them. Thanks! -- Sincerely, Yeoreum Yun