From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0CF6AC43381 for ; Thu, 14 Mar 2019 03:45:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC8C82085A for ; Thu, 14 Mar 2019 03:45:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727076AbfCNDpQ (ORCPT ); Wed, 13 Mar 2019 23:45:16 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:39900 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726746AbfCNDpQ (ORCPT ); Wed, 13 Mar 2019 23:45:16 -0400 Received: from pps.filterd (m0098420.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x2E3dfnd157095 for ; Wed, 13 Mar 2019 23:45:14 -0400 Received: from e06smtp02.uk.ibm.com (e06smtp02.uk.ibm.com [195.75.94.98]) by mx0b-001b2d01.pphosted.com with ESMTP id 2r7d804dyy-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 13 Mar 2019 23:45:14 -0400 Received: from localhost by e06smtp02.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 14 Mar 2019 03:45:08 -0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x2E3j7Wo20906200 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 14 Mar 2019 03:45:07 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7388F11C050; Thu, 14 Mar 2019 03:45:07 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9704311C04A; Thu, 14 Mar 2019 03:45:04 +0000 (GMT) Received: from skywalker.linux.ibm.com (unknown [9.199.45.189]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 14 Mar 2019 03:45:04 +0000 (GMT) X-Mailer: emacs 26.1 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: Dan Williams Cc: Jan Kara , linux-nvdimm , Michael Ellerman , Linux Kernel Mailing List , Linux MM , Ross Zwisler , Andrew Morton , linuxppc-dev , "Kirill A . Shutemov" Subject: Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default In-Reply-To: References: <20190228083522.8189-1-aneesh.kumar@linux.ibm.com> <20190228083522.8189-2-aneesh.kumar@linux.ibm.com> <87k1hc8iqa.fsf@linux.ibm.com> Date: Thu, 14 Mar 2019 09:15:02 +0530 MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 x-cbid: 19031403-0008-0000-0000-000002CD0D89 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19031403-0009-0000-0000-000022390DF9 Message-Id: <871s3aqfup.fsf@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-14_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903140023 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dan Williams writes: > On Wed, Mar 6, 2019 at 1:18 AM Aneesh Kumar K.V > wrote: >> >> Dan Williams writes: >> >> > On Thu, Feb 28, 2019 at 1:40 AM Oliver wrote: >> >> >> >> On Thu, Feb 28, 2019 at 7:35 PM Aneesh Kumar K.V >> >> wrote: >> >> > >> >> > Add a flag to indicate the ability to do huge page dax mapping. On architecture >> >> > like ppc64, the hypervisor can disable huge page support in the guest. In >> >> > such a case, we should not enable huge page dax mapping. This patch adds >> >> > a flag which the architecture code will update to indicate huge page >> >> > dax mapping support. >> >> >> >> *groan* >> >> >> >> > Architectures mostly do transparent_hugepage_flag = 0; if they can't >> >> > do hugepages. That also takes care of disabling dax hugepage mapping >> >> > with this change. >> >> > >> >> > Without this patch we get the below error with kvm on ppc64. >> >> > >> >> > [ 118.849975] lpar: Failed hash pte insert with error -4 >> >> > >> >> > NOTE: The patch also use >> >> > >> >> > echo never > /sys/kernel/mm/transparent_hugepage/enabled >> >> > to disable dax huge page mapping. >> >> > >> >> > Signed-off-by: Aneesh Kumar K.V >> >> > --- >> >> > TODO: >> >> > * Add Fixes: tag >> >> > >> >> > include/linux/huge_mm.h | 4 +++- >> >> > mm/huge_memory.c | 4 ++++ >> >> > 2 files changed, 7 insertions(+), 1 deletion(-) >> >> > >> >> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> >> > index 381e872bfde0..01ad5258545e 100644 >> >> > --- a/include/linux/huge_mm.h >> >> > +++ b/include/linux/huge_mm.h >> >> > @@ -53,6 +53,7 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr, >> >> > pud_t *pud, pfn_t pfn, bool write); >> >> > enum transparent_hugepage_flag { >> >> > TRANSPARENT_HUGEPAGE_FLAG, >> >> > + TRANSPARENT_HUGEPAGE_DAX_FLAG, >> >> > TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, >> >> > TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, >> >> > TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, >> >> > @@ -111,7 +112,8 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma) >> >> > if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG)) >> >> > return true; >> >> > >> >> > - if (vma_is_dax(vma)) >> >> > + if (vma_is_dax(vma) && >> >> > + (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_DAX_FLAG))) >> >> > return true; >> >> >> >> Forcing PTE sized faults should be fine for fsdax, but it'll break >> >> devdax. The devdax driver requires the fault size be >= the namespace >> >> alignment since devdax tries to guarantee hugepage mappings will be >> >> used and PMD alignment is the default. We can probably have devdax >> >> fall back to the largest size the hypervisor has made available, but >> >> it does run contrary to the design. Ah well, I suppose it's better off >> >> being degraded rather than unusable. >> > >> > Given this is an explicit setting I think device-dax should explicitly >> > fail to enable in the presence of this flag to preserve the >> > application visible behavior. >> > >> > I.e. if device-dax was enabled after this setting was made then I >> > think future faults should fail as well. >> >> Not sure I understood that. Now we are disabling the ability to map >> pages as huge pages. I am now considering that this should not be >> user configurable. Ie, this is something that platform can use to avoid >> dax forcing huge page mapping, but if the architecture can enable huge >> dax mapping, we should always default to using that. > > No, that's an application visible behavior regression. The side effect > of this setting is that all huge-page configured device-dax instances > must be disabled. So if the device was created with a nd_pfn->align value of PMD_SIZE, that is an indication that we would map the pages in PMD_SIZE? Ok with that understanding, If the align value is not a supported mapping size, we fail initializing the device. > >> Now w.r.t to failures, can device-dax do an opportunistic huge page >> usage? > > device-dax explicitly disclaims the ability to do opportunistic mappings. > >> I haven't looked at the device-dax details fully yet. Do we make the >> assumption of the mapping page size as a format w.r.t device-dax? Is that >> derived from nd_pfn->align value? > > Correct. > >> >> Here is what I am working on: >> 1) If the platform doesn't support huge page and if the device superblock >> indicated that it was created with huge page support, we fail the device >> init. > > Ok. > >> 2) Now if we are creating a new namespace without huge page support in >> the platform, then we force the align details to PAGE_SIZE. In such a >> configuration when handling dax fault even with THP enabled during >> the build, we should not try to use hugepage. This I think we can >> achieve by using TRANSPARENT_HUGEPAEG_DAX_FLAG. > > How is this dynamic property communicated to the guest? via device tree on powerpc. We have a device tree node indicating supported page sizes. > >> >> Also even if the user decided to not use THP, by >> echo "never" > transparent_hugepage/enabled , we should continue to map >> dax fault using huge page on platforms that can support huge pages. >> >> This still doesn't cover the details of a device-dax created with >> PAGE_SIZE align later booted with a kernel that can do hugepage dax.How >> should we handle that? That makes me think, this should be a VMA flag >> which got derived from device config? May be use VM_HUGEPAGE to indicate >> if device should use a hugepage mapping or not? > > device-dax configured with PAGE_SIZE always gets PAGE_SIZE mappings. Now what will be page size used for mapping vmemmap? Architectures possibly will use PMD_SIZE mapping if supported for vmemmap. Now a device-dax with struct page in the device will have pfn reserve area aligned to PAGE_SIZE with the above example? We can't map that using PMD_SIZE page size? -aneesh