From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp1040.oracle.com (userp1040.oracle.com [156.151.31.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3y62zh1CtlzDqNm for ; Wed, 4 Oct 2017 02:30:39 +1100 (AEDT) Subject: Re: [PATCH v9 08/12] mm: zero reserved and unavailable struct pages To: Michal Hocko Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, kasan-dev@googlegroups.com, borntraeger@de.ibm.com, heiko.carstens@de.ibm.com, davem@davemloft.net, willy@infradead.org, ard.biesheuvel@linaro.org, mark.rutland@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, sam@ravnborg.org, mgorman@techsingularity.net, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, bob.picco@oracle.com References: <20170920201714.19817-1-pasha.tatashin@oracle.com> <20170920201714.19817-9-pasha.tatashin@oracle.com> <20171003131817.omzbam3js67edp3s@dhcp22.suse.cz> From: Pasha Tatashin Message-ID: <691dba28-718c-e9a9-d006-88505eb5cd7e@oracle.com> Date: Tue, 3 Oct 2017 11:29:16 -0400 MIME-Version: 1.0 In-Reply-To: <20171003131817.omzbam3js67edp3s@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 10/03/2017 09:18 AM, Michal Hocko wrote: > On Wed 20-09-17 16:17:10, Pavel Tatashin wrote: >> Some memory is reserved but unavailable: not present in memblock.memory >> (because not backed by physical pages), but present in memblock.reserved. >> Such memory has backing struct pages, but they are not initialized by going >> through __init_single_page(). > > Could you be more specific where is such a memory reserved? > I know of one example: trim_low_memory_range() unconditionally reserves from pfn 0, but e820__memblock_setup() might provide the exiting memory from pfn 1 (i.e. KVM). But, there could be more based on this comment from linux/page-flags.h: 19 * PG_reserved is set for special pages, which can never be swapped out. Some 20 * of them might not even exist (eg empty_bad_page)... Pasha