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

Pasha Tatashin
2017-08-11T15:14:44Z

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 :) ).