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=-3.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_MED, USER_AGENT_NEOMUTT 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 30280C4321D for ; Thu, 23 Aug 2018 08:21:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D554E208D6 for ; Thu, 23 Aug 2018 08:21:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="EwzSpXLC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D554E208D6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=shutemov.name 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 S1729748AbeHWLtt (ORCPT ); Thu, 23 Aug 2018 07:49:49 -0400 Received: from mail-pf1-f193.google.com ([209.85.210.193]:33157 "EHLO mail-pf1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728096AbeHWLts (ORCPT ); Thu, 23 Aug 2018 07:49:48 -0400 Received: by mail-pf1-f193.google.com with SMTP id d4-v6so2336830pfn.0 for ; Thu, 23 Aug 2018 01:21:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=jmo0+uf6Nq5OQ3x30/PXzdsoF2UdQTxUC0+1PBESmhM=; b=EwzSpXLCjvurEVf53wHGIELJlRMLxokVIzlANondKQ882F7W8qupStUhUzZd3hb+cV 2wvbg6gnxyB+6t/akASos73k6cFyEr+9jVkSbkvsXh4f8qiknqXkLC2Gqgzhh61nlYZt Z/+JPw4IV/tLjUI3TAaoPAIjkc73bTFc8Pbri3hXXyfcWTooqEvqTk6h9b5qJBwTsyer 4/i6g8U8/Grg587W0wQc2pwMWJQORDqb7NSYvQi5NPXvhiG+BPyTj4fpz9M7c7UUkZn5 Jb2SuTtc9maggEGYxN8Y9iCwJf/OhlL34ij50Imad+9RHfhT+ANff8ZueG0R7MMk8jET iQKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=jmo0+uf6Nq5OQ3x30/PXzdsoF2UdQTxUC0+1PBESmhM=; b=b4og20LEpKlasrzCq65TtWvRfGoiUZq8BE4UGlk34bvVNKu5HjTEx0TrFu7YDa8ZFi cLA6LrfE7opHoU013hQStBvtfqWHvhOEBzpct7ATw9wwh14QuafhHYMxJQP+EL1HROhm pWS0rsrtrga+AmzqXW+beiFmfc14w0Q0aInL1GpaS5HM2ecRutVwooMuX+Nu2Gv16PM7 R+Fg3+dEF3aMpaVozNbjAMHHTlYDoWoydyPjdUeVO5HANlgQQjZaAyNDjoepakZibtZE zwhnvLBiMthtG8sZQOr/grKQjeZqAyfheqYcyxPyujwa2r+aWUq+DQYR+TKxkPV90hvX pcsA== X-Gm-Message-State: AOUpUlHOQULxfMgFRN3tEpBJz2U0Yw+TaVS22cznNxK8N5VmsA7dDREO nnXe3OjjMxj53fKM9RPQcbHPFQ== X-Google-Smtp-Source: AA+uWPzkKXPCE1+IsL393eRrDc45XNwJGHnxAVoSTeNUphXIIsKuWlFex6076NaV+Z/2FKgGJ8/mOw== X-Received: by 2002:a62:4083:: with SMTP id f3-v6mr61885359pfd.229.1535012478988; Thu, 23 Aug 2018 01:21:18 -0700 (PDT) Received: from kshutemo-mobl1.localdomain ([192.55.54.41]) by smtp.gmail.com with ESMTPSA id p26-v6sm6616514pfi.183.2018.08.23.01.21.17 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Aug 2018 01:21:17 -0700 (PDT) Received: by kshutemo-mobl1.localdomain (Postfix, from userid 1000) id DBAB43000BE; Thu, 23 Aug 2018 11:21:12 +0300 (+03) Date: Thu, 23 Aug 2018 11:21:12 +0300 From: "Kirill A. Shutemov" To: Michal Hocko Cc: Mike Kravetz , kbuild test robot , kbuild-all@01.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" , =?utf-8?B?SsOpcsO0bWU=?= 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: <20180823082112.xln7rinqcwt54teg@kshutemo-mobl1> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180823073035.GT29735@dhcp22.suse.cz> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Kirill A. Shutemov