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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 8ADDEC46477 for ; Fri, 14 Jun 2019 06:21:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6AC5220851 for ; Fri, 14 Jun 2019 06:21:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725780AbfFNGVk (ORCPT ); Fri, 14 Jun 2019 02:21:40 -0400 Received: from verein.lst.de ([213.95.11.211]:44340 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725774AbfFNGVj (ORCPT ); Fri, 14 Jun 2019 02:21:39 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id 105CE68B02; Fri, 14 Jun 2019 08:21:11 +0200 (CEST) Date: Fri, 14 Jun 2019 08:21:10 +0200 From: Christoph Hellwig To: Jason Gunthorpe Cc: Christoph Hellwig , Dan Williams , =?iso-8859-1?B?Suly9G1l?= Glisse , Ben Skeggs , "linux-mm@kvack.org" , "nouveau@lists.freedesktop.org" , "dri-devel@lists.freedesktop.org" , "linux-nvdimm@lists.01.org" , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 04/22] mm: don't clear ->mapping in hmm_devmem_free Message-ID: <20190614062110.GF7246@lst.de> References: <20190613094326.24093-1-hch@lst.de> <20190613094326.24093-5-hch@lst.de> <20190613190501.GQ22062@mellanox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190613190501.GQ22062@mellanox.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, Jun 13, 2019 at 07:05:07PM +0000, Jason Gunthorpe wrote: > Hurm, is hmm following this comment from mm_types.h? > > * If you allocate the page using alloc_pages(), you can use some of the > * space in struct page for your own purposes. The five words in the main > * union are available, except for bit 0 of the first word which must be > * kept clear. Many users use this word to store a pointer to an object > * which is guaranteed to be aligned. If you use the same storage as > * page->mapping, you must restore it to NULL before freeing the page. > > Maybe the assumption was that a driver is using ->mapping ? Maybe. The union layou in struct page certainly doesn't help..