linux-kernel - Re: [v6 01/15] x86/mm: reserve only exiting low pages

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Message-ID: <20170814114011.GG19063@dhcp22.suse.cz>
Date:   Mon, 14 Aug 2017 13:40:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pasha Tatashin <pasha.tatashin@...cle.com>
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,
        will.deacon@....com, catalin.marinas@....com, sam@...nborg.org
Subject: Re: [v6 01/15] x86/mm: reserve only exiting low pages

On Fri 11-08-17 11:24:55, Pasha Tatashin wrote:
[...]
> >>In this patchset we will stop zeroing struct page memory during allocation.
> >>Therefore, this bug must be fixed in order to avoid random assert failures
> >>caused by CONFIG_DEBUG_VM_PGFLAGS triggers.
> >>
> >>The fix is to reserve memory from the first existing PFN.
> >
> >Hmm, I assume this is a result of some assert triggering, right? Which
> >one? Why don't we need the same treatment for other than x86 arch?
> 
> Correct, the pgflags asserts were triggered when we were setting reserved
> flags to struct page for PFN 0 in which was never initialized through
> __init_single_page(). The reason they were triggered is because we set all
> uninitialized memory to ones in one of the debug patches.

And why don't we need the same treatment for other architectures?
-- 
Michal Hocko
SUSE Labs