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

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Message-ID: <20180314145450.GI23100@dhcp22.suse.cz>
Date:   Wed, 14 Mar 2018 15:54:50 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing 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>,
        Daniel Vacek <neelx@...hat.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>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Revert "mm/page_alloc: fix memmap_init_zone pageblock
 alignment"

On Wed 14-03-18 14:35:12, Ard Biesheuvel wrote:
> On 14 March 2018 at 14:13, Michal Hocko <mhocko@...nel.org> wrote:
> > Does http://lkml.kernel.org/r/20180313224240.25295-1-neelx@redhat.com
> > fix your issue? From the debugging info you provided it should because
> > the patch prevents jumping backwards.
> >
> 
> The patch does fix the boot hang.
> 
> But I am concerned that we are papering over a fundamental flaw in
> memblock_next_valid_pfn().

It seems that memblock_next_valid_pfn is doing the right thing here. It
is the alignment which moves the pfn back AFAICS. I am not really
impressed about the original patch either, to be completely honest.
It just looks awfully tricky. I still didn't manage to wrap my head
around the original issue though so I do not have much better ideas to
be honest.
-- 
Michal Hocko
SUSE Labs