linux-kernel - Re: [PATCH v1] mm: relax deferred struct page requirements

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Message-ID: <CAGM2rea=_VJJ26tohWQWgfwcFVkp0gb6j1edH1kVLjtxfugf5Q@mail.gmail.com>
Date:   Tue, 19 Jun 2018 09:50:52 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     jslaby@...e.cz
Cc:     mhocko@...nel.org, Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        benh@...nel.crashing.org, paulus@...ba.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        kirill.shutemov@...ux.intel.com,
        Reza Arbab <arbab@...ux.vnet.ibm.com>, schwidefsky@...ibm.com,
        Heiko Carstens <heiko.carstens@...ibm.com>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>, tglx@...utronix.de,
        linuxppc-dev@...ts.ozlabs.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-s390@...r.kernel.org, mgorman@...hsingularity.net
Subject: Re: [PATCH v1] mm: relax deferred struct page requirements

On Sat, Jun 16, 2018 at 4:04 AM Jiri Slaby <jslaby@...e.cz> wrote:
>
> On 11/21/2017, 08:24 AM, Michal Hocko wrote:
> > On Thu 16-11-17 20:46:01, Pavel Tatashin wrote:
> >> There is no need to have ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT,
> >> as all the page initialization code is in common code.
> >>
> >> Also, there is no need to depend on MEMORY_HOTPLUG, as initialization code
> >> does not really use hotplug memory functionality. So, we can remove this
> >> requirement as well.
> >>
> >> This patch allows to use deferred struct page initialization on all
> >> platforms with memblock allocator.
> >>
> >> Tested on x86, arm64, and sparc. Also, verified that code compiles on
> >> PPC with CONFIG_MEMORY_HOTPLUG disabled.
> >
> > There is slight risk that we will encounter corner cases on some
> > architectures with weird memory layout/topology
>
> Which x86_32-pae seems to be. Many bad page state errors are emitted
> during boot when this patch is applied:

Hi Jiri,

Thank you for reporting this bug.

Because 32-bit systems are limited in the maximum amount of physical
memory, they don't need deferred struct pages. So, we can add depends
on 64BIT to DEFERRED_STRUCT_PAGE_INIT in mm/Kconfig.

However, before we do this, I want to try reproducing this problem and
root cause it, as it might expose a general problem that is not 32-bit
specific.

Thank you,
Pavel