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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 E3FD3C433FF for ; Mon, 12 Aug 2019 13:07:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD34820684 for ; Mon, 12 Aug 2019 13:07:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728819AbfHLNHD (ORCPT ); Mon, 12 Aug 2019 09:07:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60570 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726822AbfHLNHD (ORCPT ); Mon, 12 Aug 2019 09:07:03 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DDE87300895B; Mon, 12 Aug 2019 13:07:02 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id 048676FDA5; Mon, 12 Aug 2019 13:07:00 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 12 Aug 2019 15:07:02 +0200 (CEST) Date: Mon, 12 Aug 2019 15:06:59 +0200 From: Oleg Nesterov To: Song Liu Cc: Linux Kernel Mailing List , Linux MM , Andrew Morton , Matthew Wilcox , "Kirill A. Shutemov" , Kernel Team , William Kucharski , "srikar@linux.vnet.ibm.com" Subject: Re: [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped THP Message-ID: <20190812130659.GA31560@redhat.com> References: <20190807233729.3899352-1-songliubraving@fb.com> <20190807233729.3899352-6-songliubraving@fb.com> <20190808163303.GB7934@redhat.com> <770B3C29-CE8F-4228-8992-3C6E2B5487B6@fb.com> <20190809152404.GA21489@redhat.com> <3B09235E-5CF7-4982-B8E6-114C52196BE5@fb.com> <4D8B8397-5107-456B-91FC-4911F255AE11@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4D8B8397-5107-456B-91FC-4911F255AE11@fb.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Mon, 12 Aug 2019 13:07:03 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/09, Song Liu wrote: > > +void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr) > +{ > + unsigned long haddr = addr & HPAGE_PMD_MASK; > + struct vm_area_struct *vma = find_vma(mm, haddr); > + struct page *hpage = NULL; > + pmd_t *pmd, _pmd; > + spinlock_t *ptl; > + int count = 0; > + int i; > + > + if (!vma || !vma->vm_file || > + vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE) > + return; > + > + /* > + * This vm_flags may not have VM_HUGEPAGE if the page was not > + * collapsed by this mm. But we can still collapse if the page is > + * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check() > + * will not fail the vma for missing VM_HUGEPAGE > + */ > + if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE)) > + return; > + > + pmd = mm_find_pmd(mm, haddr); > + if (!pmd) > + return; > + > + /* step 1: check all mapped PTEs are to the right huge page */ > + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { > + pte_t *pte = pte_offset_map(pmd, addr); > + struct page *page; > + > + if (pte_none(*pte) || !pte_present(*pte)) > + continue; if (!pte_present(*pte)) return; you can't simply flush pmd if this page is swapped out. > + > + page = vm_normal_page(vma, addr, *pte); > + > + if (!page || !PageCompound(page)) > + return; > + > + if (!hpage) { > + hpage = compound_head(page); > + /* > + * The mapping of the THP should not change. > + * > + * Note that uprobe may change the page table, Not only uprobe can cow the page. Debugger can do. Or mmap(PROT_WRITE, MAP_PRIVATE). uprobe() is "special" because it a) it works with a foreign mm and b) it can't stop the process which uses this mm. Otherwise it could simply update the page returned by get_user_pages_remote(FOLL_FORCE), just we would need to add FOLL_WRITE and if we do this we do not even need SPLIT, that is why, say, __access_remote_vm() works without SPLIT. Oleg.