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=-4.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,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 B3564C04EBF for ; Wed, 5 Dec 2018 17:32:15 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8817B206B7 for ; Wed, 5 Dec 2018 17:32:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="VaiyVS5Z" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8817B206B7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=pxoUh02WRoYdzdm+DJTqXqGN8tNheZODpCVZu5Qf+6I=; b=VaiyVS5ZWa6VzB lg29Le/W9fx3LGsCtAKBKuso4qRrrtPjW4b+lpXZzNI/aaxW5ZUCiPAnf0H67r0txsJHBNm6BMD6Q D/5004QyviVianFn6ecSFPFuHUSeK8r9mK12gNf6BqkslzH/HH7f80RXQD1VJ5DNIIScud9YLk9Nm nELblScb4uB7Dw+uPUN6K/v8pi+/1k0gtyJ5p+BVZgPOtTpvNOY8Wn58/j1qy6zCcrOIsjTpeoWuM dvxtZYRgwtSrvJZJelwz3XLgMjhULFaQ21QnxUYXIXa3mBWZ3f8MQQ9Ia40uPDvtWV3Hrd/vTzz4K myu34ihMmfzXUJsjLhEg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gUb1x-0008I0-D8; Wed, 05 Dec 2018 17:32:13 +0000 Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gUb1l-00088G-HT; Wed, 05 Dec 2018 17:32:01 +0000 Date: Wed, 5 Dec 2018 09:32:01 -0800 From: Matthew Wilcox To: David Hildenbrand Subject: Re: [PATCH RFC 7/7] mm: better document PG_reserved Message-ID: <20181205173201.GA11646@bombadil.infradead.org> References: <20181205122851.5891-1-david@redhat.com> <20181205122851.5891-8-david@redhat.com> <20181205143510.GA17232@bombadil.infradead.org> <46d0e90f-f0bb-815e-7a5b-4429de1c502a@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <46d0e90f-f0bb-815e-7a5b-4429de1c502a@redhat.com> User-Agent: Mutt/1.9.2 (2017-12-15) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-s390@vger.kernel.org, Michal Hocko , yi.z.zhang@linux.intel.com, Stephen Rothwell , Alexander Duyck , Dan Williams , linux-kernel@vger.kernel.org, Pavel Tatashin , linux-mm@kvack.org, linux-m68k@lists.linux-m68k.org, linux-mediatek@lists.infradead.org, Miles Chen , Anthony Yznaga , linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, Andrew Morton , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org On Wed, Dec 05, 2018 at 04:05:12PM +0100, David Hildenbrand wrote: > On 05.12.18 15:35, Matthew Wilcox wrote: > > On Wed, Dec 05, 2018 at 01:28:51PM +0100, David Hildenbrand wrote: > >> I don't see a reason why we have to document "Some of them might not even > >> exist". If there is a user, we should document it. E.g. for balloon > >> drivers we now use PG_offline to indicate that a page might currently > >> not be backed by memory in the hypervisor. And that is independent from > >> PG_reserved. > > > > I think you're confused by the meaning of "some of them might not even > > exist". What this means is that there might not be memory there; maybe > > writes to that memory will be discarded, or maybe they'll cause a machine > > check. Maybe reads will return ~0, or 0, or cause a machine check. > > We just don't know what's there, and we shouldn't try touching the memory. > > If there are users, let's document it. And I need more details for that :) > > 1. machine check: if there is a HW error, we set PG_hwpoison (except > ia64 MCA, see the list) > > 2. Writes to that memory will be discarded > > Who is the user of that? When will we have such pages right now? > > 3. Reads will return ~0, / 0? > > I think this is a special case of e.g. x86? But where do we have that, > are there any user? When there are gaps in the physical memory. As in, if you put that physical address on the bus (or in a packet), no device will respond to it. Look: 00000000-00000fff : Reserved 00001000-00057fff : System RAM 00058000-00058fff : Reserved 00059000-0009dfff : System RAM 0009e000-000fffff : Reserved Those examples I gave are examples of how various different architectures respond to "no device responded to this memory access". _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv