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 E6903C433F5 for ; Thu, 5 May 2022 17:28:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1382676AbiEERbv (ORCPT ); Thu, 5 May 2022 13:31:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50846 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1382672AbiEERbk (ORCPT ); Thu, 5 May 2022 13:31:40 -0400 Received: from mail-pj1-x102e.google.com (mail-pj1-x102e.google.com [IPv6:2607:f8b0:4864:20::102e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 265825D193 for ; Thu, 5 May 2022 10:28:00 -0700 (PDT) Received: by mail-pj1-x102e.google.com with SMTP id c1-20020a17090a558100b001dca2694f23so4563423pji.3 for ; Thu, 05 May 2022 10:28:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=xg/pm+e2Qt3mW+QrtQns7UgBoy/9i7r00873gorg2Lw=; b=YMcAIbYYOrww25piOSwixN5vCkxSnL8MnbZmG99Fhk8Q8HuBkPu1RILxtkjPNXCwKb dvdqbUVWQGPcDp9qK1CgDCXfWngmIyER8PAmsmlAhAP25rUHZwW8lhMPJZd1f3lLDzvp 4W5eUoIgUAaJCVvS33M8J4MwoVeXg4XbZjst68r4DWZcimbG61pUuypzbz0ymVT15Xxb E2NVpVTTdL+Fo4rPVusgcglmsReFPM9RXqhp+CrtAvGWiagEO9fRHVtKF534l9tL+Ewn BgpXLahsZlo0ELUC21cMdn6EHVG7aF+bjQAmRj4vpaNs+qQ8qwiLMuiF+qw+QW92urZU 9cMA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=xg/pm+e2Qt3mW+QrtQns7UgBoy/9i7r00873gorg2Lw=; b=tOe11E+vxiYK9c5DLNO2fWTJIpCMNSSRf7WRWWBdPim4AgtxaU0+hRW7JP6i95qWxQ RyR36IyNJpkhVmFCwu7vYwqWxo+30guoDlwmQgO4C3f0fC4aYKcxCcsgrc4KkQ7VyCd0 XnJkeZEBFnzA4CxImdlRh0WdQLa2zRDYQ1qi62s8lT7WSuqyvsCaM2nUp1RTRhqvrizU ybj5Hon3/hIkDGUYWdzwfkOaBIcYNqrJ3pokUdif28lE36WXN+/JD1Csv1Qb5GGgfCcQ hB4dfztrq6xWhWqumIR3yVjY6WtlsNMwZZTsGUNI4mnnn3cchERW+WAZTpEi1neJSgNP 5DTg== X-Gm-Message-State: AOAM531OfdslxXePyDD1vTyb+nqGMr3jQ78DvSImijpj5nsu8RNgJLj4 X81pq7zOEJ/WnD8CiaWINVS+FcJbP9Q= X-Google-Smtp-Source: ABdhPJzPmexJWSCp3MSWPnY62KxjIUNCMkeN7mpSQusr4t0Lyx/bohCN2cfp04dRQHYHi6kLqODjtw== X-Received: by 2002:a17:90b:3b81:b0:1dc:32ac:a66b with SMTP id pc1-20020a17090b3b8100b001dc32aca66bmr7398553pjb.49.1651771679500; Thu, 05 May 2022 10:27:59 -0700 (PDT) Received: from google.com ([2620:15c:211:201:1c0c:8050:e4d3:12f5]) by smtp.gmail.com with ESMTPSA id t2-20020a170902b20200b0015e8d4eb1c0sm1822492plr.10.2022.05.05.10.27.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 May 2022 10:27:59 -0700 (PDT) Sender: Minchan Kim Date: Thu, 5 May 2022 10:27:57 -0700 From: Minchan Kim To: Mike Kravetz Cc: David Hildenbrand , Andrew Morton , linux-mm , LKML , John Hubbard , John Dias Subject: Re: [PATCH] mm: fix is_pinnable_page against on cma page Message-ID: References: <20220502173558.2510641-1-minchan@kernel.org> <29d0c1c3-a44e-4573-7e7e-32be07544dbe@redhat.com> <08e9855c-395d-f40c-de3d-1ec8b644bfe8@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 05, 2022 at 10:00:07AM -0700, Mike Kravetz wrote: > On 5/4/22 23:48, Minchan Kim wrote: > > On Wed, May 04, 2022 at 03:48:54PM -0700, Minchan Kim wrote: > >> On Tue, May 03, 2022 at 06:02:33PM +0200, David Hildenbrand wrote: > >>> On 03.05.22 17:26, Minchan Kim wrote: > >>>> On Tue, May 03, 2022 at 03:15:24AM +0200, David Hildenbrand wrote: > >>>>> > >>>>>>>>> However, I assume we have the same issue right now already with > >>>>>>> ZONE_MOVABLE and MIGRATE_CMA when trying to pin a page residing on these > >>>>>> > >>>>>> ZONE_MOVALBE is also changed dynamically? > >>>>>> > >>>>> > >>>>> Sorry, with "same issue" I meant failing to pin if having to migrate and > >>>>> the page is temporarily unmovable. > >>>>> > >>>>>>> there are temporarily unmovable and we fail to migrate. But it would now > >>>>>>> apply even without ZONE_MOVABLE or MIGRATE_CMA. Hm... > >>>>>> > >>>>>> Didn't parse your last mention. > >>>>> > >>>>> On a system that neither uses ZONE_MOVABLE nor MIGRATE_CMA we might have > >>>>> to migrate now when pinning. > >>>> > >>>> I don't understand your point. My problem is pin_user_pages with > >>>> FOLL_LONGTERM. It shouldn't pin a page from ZONE_MOVABLE and cma area > >>>> without migrating page out of movable zone or CMA area. > >>>> That's why try_grab_folio checks whether target page stays in those > >>>> movable areas. However, to check CMA area, is_migrate_cma_page is > >>>> racy so the FOLL_LONGTERM flag semantic is broken right now. > >>>> > >>>> Do you see any problem of the fix? > >>> > >>> My point is that you might decide to migrate a page because you stumble > >>> over MIGRATE_ISOLATE, although there is no need to reject long-term > >>> pinning and to trigger page migration. > >>> > >>> Assume a system without ZONE_MOVABLE and without MIGRATE_CMA. Assume > >>> someone reserves gigantic pages (alloc_contig_range()) and you have > >>> concurrent long-term pinning on a page that is no MIGRATE_ISOLATE. > >>> > >>> GUP would see MIGRATE_ISOLATE and would reject pinning. The page has to > >>> be migrated, which can fail if the page is temporarily unmovable. > >> > >> A dump question since I'm not familiar with hugetlb. > >> > >> Is above reasonable scenario? > >> > >> The gigantic page is about to be created using alloc_contig_range so > >> they has MIGRATE_ISOLATE as temporal state. It means no one uses the > >> page yet so I guess the page is not mapped at userspace but other is > >> trying to access the page using pin_user_pages? > >> > > > > Too dump question. Never mind. > > Posted v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@kernel.org/T/#u > > > > Well your question mentioned hugetlb so my mail filters caught it :) > > Your question caused me to think of the following. No need for any immediate > change: I think. Just wanted to share. > > Suppose someone has reserved CMA for gigantic hugetlb allocations. And, > suppose FOLL_LONGTERM is attempted on such a page (it would be in use). The > desired action would be to migrate the page out of CMA. Correct? > > Gigantic pages can only be migrated IF there is another (already allocated) > gigantic page available. The routine to try and allocate a page 'on the fly' > for migration will fail if passed a gigantic size. There 'might' be a free > pre-allocated gigantic page. However, if the user set up CMA reserves for > gigantic page allocations it is likely the free gigantic page is also in CMA. > Therefore, it can not be used for this migration. So, unless my reasoning > is wrong, FOLL_LONGTERM would almost always fail for gigantic pages in CMA. FOLL_LONGTERM on CMA-backed gigantic page would already fail, Thanks for sharing! Anyway, David's concern was non-CMA-backed gigantic page. The alloc_contig_range with MIGRATE_ISOLATE runs with concurrent FOLL_LONGTERM pinning, which could trigger page migration we didn't have before so it might increase FOLL_LONGTERM GUP failure rate.