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

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Message-ID: <23e22449-89f0-507d-e92a-9ee947a7c363@oracle.com>
Date:   Fri, 11 Aug 2017 11:13:07 -0400
From:   Pasha Tatashin <pasha.tatashin@...cle.com>
To:     Michal Hocko <mhocko@...nel.org>
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 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.

> 
>> - Never set any fields in struct pages before they are initialized
>> - Zero struct page at the beginning of struct page initialization
> 
> Please give us a more highlevel description of how your reimplementation
> works and how is the patchset organized. I will go through those patches
> but it is always good to give an overview in the cover letter to make
> the review easier.

Ok, will add more explanation to the cover letter.

>> Single threaded struct page init: 7.6s/T improvement
>> Deferred struct page init: 10.2s/T improvement
> 
> What are before and after numbers and how have you measured them.

When I send out this series the next time I will include before vs. 
after on the machine I tested, including links to dmesg output.

I used my early boot timestamps for x86 and sparc to measure the data. 
Early boot timestamps for sparc is already part of mainline, the x86 
patches are out for review: https://lkml.org/lkml/2017/8/10/946 (should 
have changed subject line there :) ).