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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FB0BECAAD4 for ; Thu, 1 Sep 2022 01:24:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EF1396B0072; Wed, 31 Aug 2022 21:24:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EA04A8D0001; Wed, 31 Aug 2022 21:24:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D67A36B0074; Wed, 31 Aug 2022 21:24:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id C81FA6B0072 for ; Wed, 31 Aug 2022 21:24:37 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 9A2251C6346 for ; Thu, 1 Sep 2022 01:24:37 +0000 (UTC) X-FDA: 79861771794.20.7C532DE Received: from out30-54.freemail.mail.aliyun.com (out30-54.freemail.mail.aliyun.com [115.124.30.54]) by imf01.hostedemail.com (Postfix) with ESMTP id 6ECE040037 for ; Thu, 1 Sep 2022 01:24:34 +0000 (UTC) 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 ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=none; spf=pass (imf01.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.54 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1661995477; a=rsa-sha256; cv=none; b=0BKXT8GLqW692v00WCd4XFqNIVHEx7EXrN1MKhYlkTDXQcmHmQH96hrqnjg0Wq9LzHK+dI h/TU385iEtJ0BTr6wIiaAe0l/ihievqws5A44dCZKR8ajV2TNzdE3l7drxMIZ4u8Pd9/GP 2nICWLhcFHiwLg8i+YydvEXR2stIeyw= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661995477; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=IbkaFeKxuzS8C3R6cXY4RSCMGeeDaaP4uDpSASLp8dk=; b=ge6VDVUyIqLn2MXl4fULEP9CvMtlfPpIBZhO6LhpVRRN7FefdF8xcii5mVc/+ujzjLeUvG O6/+mtYZOyCCFe7vsUrHJP/zuFIPZjdJMRl9hPQ6gPbxGGSDUu/QYJez6lcueqyaDdgSRx BDYZDoot4tHMLvtxChQA+tozRpxC7Lo= X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6ECE040037 X-Rspam-User: Authentication-Results: imf01.hostedemail.com; dkim=none; spf=pass (imf01.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.54 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com X-Stat-Signature: 8gt5gp4z9xomfaeywbtyotwxw4ticf3r X-HE-Tag: 1661995474-343126 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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.