linux-kernel - Re: [v6 00/15] complete deferred page initialization

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Date:   Fri, 11 Aug 2017 17:22:41 +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 00/15] complete deferred page initialization

On Fri 11-08-17 11:13:07, Pasha Tatashin wrote:
> On 08/11/2017 03:58 AM, Michal Hocko wrote:
> >[I am sorry I didn't get to your previous versions]
> 
> Thank you for reviewing this work. I will address your comments, and
> send-out a new patches.
> 
> >>
> >>In this work we do the following:
> >>- Never read access struct page until it was initialized
> >
> >How is this enforced? What about pfn walkers? E.g. page_ext
> >initialization code (page owner in particular)
> 
> This is hard to enforce 100%. But, because we have a patch in this series
> that sets all memory that was allocated by memblock_virt_alloc_try_nid_raw()
> to ones with debug options enabled, and because Linux has a good set of
> asserts in place that check struct pages to be sane, especially the ones
> that are enabled with this config: CONFIG_DEBUG_VM_PGFLAGS. I was able to
> find many places in linux which accessed struct pages before
> __init_single_page() is performed, and fix them. Most of these places happen
> only when deferred struct page initialization code is enabled.

Yes, I am very well aware of how hard is this to guarantee. I was merely
pointing out that the changelog should be more verbose about your
testing and assumptions so that we can revalidate them.
-- 
Michal Hocko
SUSE Labs