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Date: Mon, 5 Nov 2018 18:20:24 -0800
From: Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: Re: [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work
Message-ID: <20181106022024.ndn377ze6xljsxkb@ca-dmjordan1.us.oracle.com>
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 <FC2EB02D-3D05-4A13-A92E-4171B37B15BA@cs.rutgers.edu>
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To: Zi Yan <zi.yan@cs.rutgers.edu>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>, linux-mm@kvack.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, aarcange@redhat.com, aaron.lu@intel.com, akpm@linux-foundation.org, alex.williamson@redhat.com, bsd@redhat.com, darrick.wong@oracle.com, dave.hansen@linux.intel.com, jgg@mellanox.com, jwadams@google.com, jiangshanlai@gmail.com, mhocko@kernel.org, mike.kravetz@oracle.com, Pavel.Tatashin@microsoft.com, prasad.singamsetty@oracle.com, rdunlap@infradead.org, steven.sistare@oracle.com, tim.c.chen@intel.com, tj@kernel.org, vbabka@suse.cz

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