linux-kernel - Re: [PATCH v2] Revert "mm/page_alloc: fix memmap_init

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Message-ID: <20180315183506.GT23100@dhcp22.suse.cz>
Date:   Thu, 15 Mar 2018 19:35:06 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Daniel Vacek <neelx@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Paul Burton <paul.burton@...tec.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] Revert "mm/page_alloc: fix memmap_init_zone pageblock
 alignment"

On Thu 15-03-18 11:28:27, Linus Torvalds wrote:
> On Thu, Mar 15, 2018 at 11:21 AM, Michal Hocko <mhocko@...nel.org> wrote:
> >
> > Well, pfn_valid says that a given pfn is backed by a real memory and it
> > has a valid struct page backing it.
> 
> No, it really just says the latter. There should be a "struct page" for it.

You are right! A simple example could be non volatile memory. That is
certainly not RAM but it has pfn_valid memory. Sorry about the
confusion.
-- 
Michal Hocko
SUSE Labs