linux-kernel - Re: [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work

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Message-ID: <20181106022024.ndn377ze6xljsxkb@ca-dmjordan1.us.oracle.com>
Date:   Mon, 5 Nov 2018 18:20:24 -0800
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Zi Yan <zi.yan@...rutgers.edu>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>, linux-mm@...ck.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        aarcange@...hat.com, aaron.lu@...el.com, akpm@...ux-foundation.org,
        alex.williamson@...hat.com, bsd@...hat.com,
        darrick.wong@...cle.com, dave.hansen@...ux.intel.com,
        jgg@...lanox.com, jwadams@...gle.com, jiangshanlai@...il.com,
        mhocko@...nel.org, mike.kravetz@...cle.com,
        Pavel.Tatashin@...rosoft.com, prasad.singamsetty@...cle.com,
        rdunlap@...radead.org, steven.sistare@...cle.com,
        tim.c.chen@...el.com, tj@...nel.org, vbabka@...e.cz
Subject: Re: [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work

Hi Zi,

On Mon, Nov 05, 2018 at 01:49:14PM -0500, Zi Yan wrote:
> On 5 Nov 2018, at 11:55, Daniel Jordan wrote:
>
> Do you think if it makes sense to use ktask for huge page migration (the data
> copy part)?

It certainly could.

> I did some experiments back in 2016[1], which showed that migrating one 2MB page
> with 8 threads could achieve 2.8x throughput of the existing single-threaded method.
> The problem with my parallel page migration patchset at that time was that it
> has no CPU-utilization awareness, which is solved by your patches now.

Did you run with fewer than 8 threads?  I'd want a bigger speedup than 2.8x for
8, and a smaller thread count might improve thread utilization.

It would be nice to multithread at a higher granularity than 2M, too: a range
of THPs might also perform better than a single page.

Thanks for your comments.

> [1]https://lkml.org/lkml/2016/11/22/457