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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 14F17C18E5A for ; Tue, 10 Mar 2020 12:00:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE3932464B for ; Tue, 10 Mar 2020 11:59:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583841599; bh=l0GPZ7rgbbX42aXiVWrJZANgIIl3Aa/6T0DuOcGTUrQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=qXvgsM5iMNIaVTCIi+wmybrLJtkS7xlXkGfoSNNo1ohQ78alILXGlakYT1lbmXFst IPD/6086njLHHQRdX0/2rDHHPresrKUmBkziHFouC4eHZBch/VCOkzULRNUkMlUJb6 lXif247SVAz4RQx1LP0XyT8W9eiRWosM2l1Wf1rA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726510AbgCJL76 (ORCPT ); Tue, 10 Mar 2020 07:59:58 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:39360 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726252AbgCJL76 (ORCPT ); Tue, 10 Mar 2020 07:59:58 -0400 Received: by mail-wm1-f66.google.com with SMTP id f7so1032294wml.4; Tue, 10 Mar 2020 04:59:56 -0700 (PDT) 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; bh=0bAhm3DuaLfkzUm2lkD/QpZIHlNuTATTEEtwUNoLDMc=; b=H5WlDiIcRKRNsZ5ub5rK9FEK1l0y+mnnmFPfvMMGzXM2eL7qth29CXc387NxexQQ7n wYdePWPXJZx5VJc0SwcHeTVSCvB8YvjWNbSfV1uNHmgxS9eSxVpW9K8jboR2DeN4Qikf p0z7BhuLhxw3u+zpJrO+Q35OhtS6m44KWlXaHbuL1HANYxvFHFccsJXo/xTmDJD56A/V 86DuETJgTRZ3sF+8l4zcVI+GpnzdxfLuM1uCzLzitz83ha5fjAX4Dp6/GR2duy0xnILC wsuOpektqHgPV5m2SfIgU7MeZjyVPUH2K0ux1Gzn374yzPe7srIt9gDQiAcKl0n0UnFf HvcQ== X-Gm-Message-State: ANhLgQ1Q2LGAYQEyPG42iPmuwBTPu77IA8UqbJFz9s7mNAPVa65DSXKh UmnGekSOI+GU0B++Ehr6WjQ= X-Google-Smtp-Source: ADFU+vuTmNn8vy4JGsoYYV4PMEgdh1palpn0A7Ri4XkzIOQ/sbHDPtvrJg+BmE/NgDS3Qt080LephA== X-Received: by 2002:a7b:c20c:: with SMTP id x12mr1914581wmi.80.1583841596287; Tue, 10 Mar 2020 04:59:56 -0700 (PDT) Received: from localhost (prg-ext-pat.suse.com. [213.151.95.130]) by smtp.gmail.com with ESMTPSA id m21sm3763917wmi.27.2020.03.10.04.59.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Mar 2020 04:59:55 -0700 (PDT) Date: Tue, 10 Mar 2020 12:59:55 +0100 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, Andrew Morton , "Michael S . Tsirkin" , Jason Wang , Oscar Salvador , Igor Mammedov , Dave Young , Dan Williams , Pavel Tatashin , Stefan Hajnoczi , Vlastimil Babka Subject: Re: [PATCH v1 07/11] virtio-mem: Allow to offline partially unplugged memory blocks Message-ID: <20200310115955.GI8447@dhcp22.suse.cz> References: <20200302134941.315212-1-david@redhat.com> <20200302134941.315212-8-david@redhat.com> <20200310114312.GG8447@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 10-03-20 12:46:05, David Hildenbrand wrote: > On 10.03.20 12:43, Michal Hocko wrote: > > On Mon 02-03-20 14:49:37, David Hildenbrand wrote: > > [...] > >> +static void virtio_mem_notify_going_offline(struct virtio_mem *vm, > >> + unsigned long mb_id) > >> +{ > >> + const unsigned long nr_pages = PFN_DOWN(vm->subblock_size); > >> + unsigned long pfn; > >> + int sb_id, i; > >> + > >> + for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) { > >> + if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1)) > >> + continue; > >> + /* > >> + * Drop our reference to the pages so the memory can get > >> + * offlined and add the unplugged pages to the managed > >> + * page counters (so offlining code can correctly subtract > >> + * them again). > >> + */ > >> + pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) + > >> + sb_id * vm->subblock_size); > >> + adjust_managed_page_count(pfn_to_page(pfn), nr_pages); > >> + for (i = 0; i < nr_pages; i++) > >> + page_ref_dec(pfn_to_page(pfn + i)); > > > > Is there ever situation this might be a different than 1->0 transition? > > Only if some other code would be taking a reference. At least not from > virtio-mem perspective. OK, so that is essentially an error condition. I think it shouldn't go silent and you want something like if (WARN_ON(!page_ref_sub_and_test(page))) dump_page(pfn_to_page(pfn + i), "YOUR REASON"); -- Michal Hocko SUSE Labs