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Date: Tue, 3 Oct 2017 11:29:16 -0400 From: Pasha Tatashin <pasha.tatashin@...cle.com> To: Michal Hocko <mhocko@...nel.org> Cc: linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org, linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, x86@...nel.org, kasan-dev@...glegroups.com, borntraeger@...ibm.com, heiko.carstens@...ibm.com, davem@...emloft.net, willy@...radead.org, ard.biesheuvel@...aro.org, mark.rutland@....com, will.deacon@....com, catalin.marinas@....com, sam@...nborg.org, mgorman@...hsingularity.net, steven.sistare@...cle.com, daniel.m.jordan@...cle.com, bob.picco@...cle.com Subject: Re: [PATCH v9 08/12] mm: zero reserved and unavailable struct pages 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
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