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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 AE41FC4321D for ; Thu, 23 Aug 2018 10:33:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5721921532 for ; Thu, 23 Aug 2018 10:33:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5721921532 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728402AbeHWODA (ORCPT ); Thu, 23 Aug 2018 10:03:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:52230 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728206AbeHWODA (ORCPT ); Thu, 23 Aug 2018 10:03:00 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 47958ADF3; Thu, 23 Aug 2018 10:33:54 +0000 (UTC) Date: Thu, 23 Aug 2018 12:33:52 +0200 From: Michal Hocko To: "Kirill A. Shutemov" Cc: Mike Kravetz , kbuild test robot , kbuild-all@01.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" , =?iso-8859-1?B?Suly9G1l?= Glisse , Vlastimil Babka , Naoya Horiguchi , Davidlohr Bueso , Andrew Morton , stable@vger.kernel.org Subject: Re: [PATCH v3 1/2] mm: migration: fix migration of huge PMD shared pages Message-ID: <20180823103352.GZ29735@dhcp22.suse.cz> References: <20180821205902.21223-2-mike.kravetz@oracle.com> <201808220831.eM0je51n%fengguang.wu@intel.com> <975b740d-26a6-eb3f-c8ca-1a9995d0d343@oracle.com> <20180822122848.GL29735@dhcp22.suse.cz> <4a95a24f-534f-0938-f358-2a410817a412@oracle.com> <20180823073035.GT29735@dhcp22.suse.cz> <20180823082112.xln7rinqcwt54teg@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180823082112.xln7rinqcwt54teg@kshutemo-mobl1> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 23-08-18 11:21:12, Kirill A. Shutemov wrote: > On Thu, Aug 23, 2018 at 09:30:35AM +0200, Michal Hocko wrote: > > On Wed 22-08-18 09:48:16, Mike Kravetz wrote: > > > On 08/22/2018 05:28 AM, Michal Hocko wrote: > > > > On Tue 21-08-18 18:10:42, Mike Kravetz wrote: > > > > [...] > > > >> diff --git a/mm/rmap.c b/mm/rmap.c > > > >> index eb477809a5c0..8cf853a4b093 100644 > > > >> --- a/mm/rmap.c > > > >> +++ b/mm/rmap.c > > > >> @@ -1362,11 +1362,21 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > > > >> } > > > >> > > > >> /* > > > >> - * We have to assume the worse case ie pmd for invalidation. Note that > > > >> - * the page can not be free in this function as call of try_to_unmap() > > > >> - * must hold a reference on the page. > > > >> + * For THP, we have to assume the worse case ie pmd for invalidation. > > > >> + * For hugetlb, it could be much worse if we need to do pud > > > >> + * invalidation in the case of pmd sharing. > > > >> + * > > > >> + * Note that the page can not be free in this function as call of > > > >> + * try_to_unmap() must hold a reference on the page. > > > >> */ > > > >> end = min(vma->vm_end, start + (PAGE_SIZE << compound_order(page))); > > > >> + if (PageHuge(page)) { > > > >> + /* > > > >> + * If sharing is possible, start and end will be adjusted > > > >> + * accordingly. > > > >> + */ > > > >> + (void)huge_pmd_sharing_possible(vma, &start, &end); > > > >> + } > > > >> mmu_notifier_invalidate_range_start(vma->vm_mm, start, end); > > > > > > > > I do not get this part. Why don't we simply unconditionally invalidate > > > > the whole huge page range? > > > > > > In this routine, we are only unmapping a single page. The existing code > > > is limiting the invalidate range to that page size: 4K or 2M. With shared > > > PMDs, we have the possibility of unmapping a PUD_SIZE area: 1G. I don't > > > think we want to unconditionally invalidate 1G. Is that what you are asking? > > > > But we know that huge_pmd_unshare unmapped a shared pte so we know when > > to flush 2MB or 1GB. I really do not like how huge_pmd_sharing_possible > > a) duplicates some checks and b) it updates start/stop out of line. > > My reading on this is that mmu_notifier_invalidate_range_start() has to be > called from sleepable context on the full range that *can* be invalidated > before following mmu_notifier_invalidate_range_end(). > > In this case huge_pmd_unshare() may unmap aligned PUD_SIZE around the PMD > page that effectively enlarge range that has to be covered by > mmu_notifier_invalidate_range_start(). We cannot yet know if there's any > shared page tables in the range, so we need to go with worst case > scenario. > > I don't see conceptually better solution than what is proposed. I was thinking we would just pull PageHuge outside of the page_vma_mapped_walk. I thought it would look much more straightforward but I've tried to put something together and it grown into an ugly code as well. So going the Mike's way might be a better option after all. -- Michal Hocko SUSE Labs