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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,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 9C683C433B4 for ; Thu, 13 May 2021 13:15:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E680C613BF for ; Thu, 13 May 2021 13:15:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E680C613BF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4A5C66B0036; Thu, 13 May 2021 09:15:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 47C7A6B006E; Thu, 13 May 2021 09:15:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 345116B0070; Thu, 13 May 2021 09:15:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0184.hostedemail.com [216.40.44.184]) by kanga.kvack.org (Postfix) with ESMTP id 04F286B0036 for ; Thu, 13 May 2021 09:15:42 -0400 (EDT) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 95E9E181AC9C6 for ; Thu, 13 May 2021 13:15:42 +0000 (UTC) X-FDA: 78136254924.13.C5DD237 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf10.hostedemail.com (Postfix) with ESMTP id 3877140002F7 for ; Thu, 13 May 2021 13:15:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=CqhS/DjApfCwkLFCvP6kllDyz5SMs1FoNvFzUNiKyfA=; b=d8SS8qgwVEBfC/z564sa+2N9DF Wzl+TkORKwOMT+wsnvHLbotWjCbktxMqEnEd2QDACc1JoP6nuoT0gG+x6tSw0bH/nMZmg3vcFw6bk T9uVRNj0t06RnJG86r4+uzrnLHwlQSMb56hyRRPYQTBnk6U+x/MSZe3SCKnWIz/ozlPPAYy1gj+4q HvSfyuYYfdpXO5LS6n3ggU8Sml9RM0tpfiBgwZrFWjnivtBXZC1AjPstssMqYjg0jJRha16bVMCV1 kn3Rz01pS2/4jQSLQY4ZUixfzSpIiGfI8UfZ528pvwk//NUchwwjGJ7iq2xlPLP94iBxGBki80CBw OJddTV1Q==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lhBB6-009RwN-5m; Thu, 13 May 2021 13:15:10 +0000 Date: Thu, 13 May 2021 14:15:00 +0100 From: Matthew Wilcox To: Ralph Campbell Cc: linux-mm@kvack.org, kvm-ppc@vger.kernel.org, nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, Dan Williams , Ira Weiny , Jerome Glisse , John Hubbard , Alistair Popple , Christoph Hellwig , Jason Gunthorpe , Bharata B Rao , Zi Yan , "Kirill A . Shutemov" , Yang Shi , Paul Mackerras , Ben Skeggs , Andrew Morton Subject: Re: [RFC PATCH v3 0/2] mm: remove extra ZONE_DEVICE struct page refcount Message-ID: References: <20201001181715.17416-1-rcampbell@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201001181715.17416-1-rcampbell@nvidia.com> Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=d8SS8qgw; dmarc=none; spf=none (imf10.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-Stat-Signature: g4e1bbh4f3bgu8wqa9hgdrsq6shyssa1 X-Rspamd-Queue-Id: 3877140002F7 X-Rspamd-Server: rspam02 Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620911725-658314 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Oct 01, 2020 at 11:17:13AM -0700, Ralph Campbell wrote: > This is still an RFC because after looking at the pmem/dax code some > more, I realized that the ZONE_DEVICE struct pages are being inserted > into the process' page tables with vmf_insert_mixed() and a zero > refcount on the ZONE_DEVICE struct page. This is sort of OK because > insert_pfn() increments the reference count on the pgmap which is what > prevents memunmap_pages() from freeing the struct pages and it doesn't > check for a non-zero struct page reference count. > But, any calls to get_page() will hit the VM_BUG_ON_PAGE() that > checks for a reference count == 0. This seems to have gone quiet. What needs to happen to resurrect this?