linux-kernel - Re: [PATCH 0/7] padata: parallelize deferred page init

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Date:   Thu, 30 Apr 2020 18:09:35 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Michal Hocko <mhocko@...nel.org>, Pavel Machek <pavel@....cz>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Tejun Heo <tj@...nel.org>, Zi Yan <ziy@...dia.com>,
        linux-crypto@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] padata: parallelize deferred page init

On Thu, Apr 30, 2020 at 04:11:18PM -0400, Daniel Jordan wrote:
> Sometimes the kernel doesn't take full advantage of system memory
> bandwidth, leading to a single CPU spending excessive time in
> initialization paths where the data scales with memory size.
> 
> Multithreading naturally addresses this problem, and this series is the
> first step.
> 
> It extends padata, a framework that handles many parallel singlethreaded
> jobs, to handle multithreaded jobs as well by adding support for
> splitting up the work evenly, specifying a minimum amount of work that's
> appropriate for one helper thread to do, load balancing between helpers,
> and coordinating them.  More documentation in patches 4 and 7.
> 
> The first user is deferred struct page init, a large bottleneck in
> kernel boot--actually the largest for us and likely others too.  This
> path doesn't require concurrency limits, resource control, or priority
> adjustments like future users will (vfio, hugetlb fallocate, munmap)
> because it happens during boot when the system is otherwise idle and
> waiting on page init to finish.
> 
> This has been tested on a variety of x86 systems and speeds up kernel
> boot by 6% to 49% by making deferred init 63% to 91% faster.  Patch 6
> has detailed numbers.  Test results from other systems appreciated.
> 
> This series is based on v5.6 plus these three from mmotm:
> 
>   mm-call-touch_nmi_watchdog-on-max-order-boundaries-in-deferred-init.patch
>   mm-initialize-deferred-pages-with-interrupts-enabled.patch
>   mm-call-cond_resched-from-deferred_init_memmap.patch
> 
> All of the above can be found in this branch:
> 
>   git://oss.oracle.com/git/linux-dmjordan.git padata-mt-definit-v1
>   https://oss.oracle.com/git/gitweb.cgi?p=linux-dmjordan.git;a=shortlog;h=refs/heads/padata-mt-definit-v1

For the series (and the three prerequisite patches):

Tested-by: Josh Triplett <josh@...htriplett.org>

Thank you for writing this, and thank you for working towards
upstreaming it!