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Date: Wed, 14 Mar 2018 15:54:50 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Mel Gorman <mgorman@techsingularity.net>,
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        Pavel Tatashin <pasha.tatashin@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] Revert "mm/page_alloc: fix memmap_init_zone pageblock
 alignment"
Message-ID: <20180314145450.GI23100@dhcp22.suse.cz>
References: <20180314134431.13241-1-ard.biesheuvel@linaro.org>
 <20180314141323.GD23100@dhcp22.suse.cz>
 <CAKv+Gu9hrZnX6pmiCaT=S30KQ11tY4kv=qvdSPPZ2nYDC7P7eQ@mail.gmail.com>
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On Wed 14-03-18 14:35:12, Ard Biesheuvel wrote:
> On 14 March 2018 at 14:13, Michal Hocko <mhocko@kernel.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