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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CF426ECAAD1 for ; Thu, 1 Sep 2022 01:24:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232509AbiIABYh (ORCPT ); Wed, 31 Aug 2022 21:24:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37150 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232078AbiIABYf (ORCPT ); Wed, 31 Aug 2022 21:24:35 -0400 Received: from out30-57.freemail.mail.aliyun.com (out30-57.freemail.mail.aliyun.com [115.124.30.57]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DEE3214FC9E; Wed, 31 Aug 2022 18:24:33 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046051;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=11;SR=0;TI=SMTPD_---0VNtA9pB_1661995469; Received: from 30.97.48.53(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0VNtA9pB_1661995469) by smtp.aliyun-inc.com; Thu, 01 Sep 2022 09:24:30 +0800 Message-ID: Date: Thu, 1 Sep 2022 09:24:42 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0 Subject: Re: [PATCH] hugetlb: simplify hugetlb handling in follow_page_mask To: Mike Kravetz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, inuxppc-dev@lists.ozlabs.org, linux-ia64@vger.kernel.org, David Hildenbrand , "Aneesh Kumar K . V" , Naoya Horiguchi , Michael Ellerman , Muchun Song , Andrew Morton References: <20220829234053.159158-1-mike.kravetz@oracle.com> <57c8f032-e48a-bacb-7922-3e2cc10dc0d2@linux.alibaba.com> <0a8025eb-cf15-453a-7d7d-7c72d008889a@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/1/2022 8:00 AM, Mike Kravetz wrote: > On 08/31/22 09:07, Baolin Wang wrote: >> >> >> On 8/31/2022 2:39 AM, Mike Kravetz wrote: >>> On 08/30/22 09:44, Mike Kravetz wrote: >>>> On 08/30/22 09:06, Baolin Wang wrote: >>>>> Hi Mike, >>>>> >>>>> On 8/30/2022 7:40 AM, Mike Kravetz wrote: >>>>>> During discussions of this series [1], it was suggested that hugetlb >>>>>> handling code in follow_page_mask could be simplified. At the beginning >>>>>> of follow_page_mask, there currently is a call to follow_huge_addr which >>>>>> 'may' handle hugetlb pages. ia64 is the only architecture which provides >>>>>> a follow_huge_addr routine that does not return error. Instead, at each >>>>>> level of the page table a check is made for a hugetlb entry. If a hugetlb >>>>>> entry is found, a call to a routine associated with that entry is made. >>>>>> >>>>>> Currently, there are two checks for hugetlb entries at each page table >>>>>> level. The first check is of the form: >>>>>> if (p?d_huge()) >>>>>> page = follow_huge_p?d(); >>>>>> the second check is of the form: >>>>>> if (is_hugepd()) >>>>>> page = follow_huge_pd(). >>>>>> >>>>>> We can replace these checks, as well as the special handling routines >>>>>> such as follow_huge_p?d() and follow_huge_pd() with a single routine to >>>>>> handle hugetlb vmas. >>>>>> >>>>>> A new routine hugetlb_follow_page_mask is called for hugetlb vmas at the >>>>>> beginning of follow_page_mask. hugetlb_follow_page_mask will use the >>>>>> existing routine huge_pte_offset to walk page tables looking for hugetlb >>>>>> entries. huge_pte_offset can be overwritten by architectures, and already >>>>>> handles special cases such as hugepd entries. >>>>> >>>>> Could you also mention that this patch will fix the lock issue for >>>>> CONT-PTE/PMD hugetlb by changing to use huge_pte_lock()? which will help >>>>> people to understand the issue. >>>> >>>> Will update message in v2. Thanks for taking a look! >>>> >>> >>> One additional thought, we 'may' need a separate patch to fix the locking >>> issues that can be easily backported. Not sure this 'simplification' is >>> a good backport candidate. >> >> Yes, that was my thought before, but David did not like adding more >> make-legacy-cruft-happy code. >> >> So how about creating a series that contains 3 patches: picking up patch 1 >> and patch 3 of my previous series [1], and your current patch? That means >> patch 1 and patch 2 in this series can fix the lock issue explicitly and be >> suitable to backport, meanwhile patch 3 (which is your current patch) will >> cleanup the legacy code. >> > > When I looked at patch 3, I was thinking the update follow_huge_pmd routine > would work for the PTE level with a few more modifications. Perhaps, this is > too ugly but it is a smaller set of changes for backport. > > Of course, this would be followed up with the simplification patch which > removes all this code. Yes, looks more simple. I can send you a formal patch with your suggestion, which can be added into your cleanup series. Thanks.