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From: "Zi Yan" <zi.yan@cs.rutgers.edu>
Subject: Re: [RFC 1/2] Protect larger order pages from breaking up
Date: Thu, 22 Feb 2018 16:53:25 -0500
Message-ID: <E4FA7972-B97C-4D63-8473-C6F1F4FAB7A0@cs.rutgers.edu>
In-Reply-To: <68050f0f-14ca-d974-9cf4-19694a2244b9@schoebel-theuer.de>
References: <20180216160110.641666320@linux.com>
 <20180216160121.519788537@linux.com>
 <20180219101935.cb3gnkbjimn5hbud@techsingularity.net>
 <68050f0f-14ca-d974-9cf4-19694a2244b9@schoebel-theuer.de>
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To: Thomas Schoebel-Theuer <tst@schoebel-theuer.de>
Cc: Mel Gorman <mgorman@techsingularity.net>, Christoph Lameter <cl@linux.com>, Matthew Wilcox <willy@infradead.org>, linux-mm@kvack.org, linux-rdma@vger.kernel.org, akpm@linux-foundation.org, andi@firstfloor.org, Rik van Riel <riel@redhat.com>, Michal Hocko <mhocko@kernel.org>, Guy Shattah <sguy@mellanox.com>, Anshuman Khandual <khandual@linux.vnet.ibm.com>, Michal Nazarewicz <mina86@mina86.com>, Vlastimil Babka <vbabka@suse.cz>, David Nellans <dnellans@nvidia.com>, Laura Abbott <labbott@redhat.com>, Pavel Machek <pavel@ucw.cz>, Dave Hansen <dave.hansen@intel.com>, Mike Kravetz <mike.kravetz@oracle.com>

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On 22 Feb 2018, at 16:19, Thomas Schoebel-Theuer wrote:

<snip>
>
> No need for a deep understanding of the theory of the memory fragmentat=
ion problem.
>
> Also no need for adding anything to the boot commandline. Fragmentation=
 will typically occur only after some days or weeks or months of operatio=
n, at least in all of the practical cases I have personally seen at 1&1 d=
atacenters and their workloads.
>
> Please notice that fragmentation can be a very serious problem for oper=
ations if you are hurt by it. It can seriously harm your business. And it=
 is _extremely_ specific to the actual workload, and to the hardware / ch=
ipset / etc. This is addressed by the above method of determining the rig=
ht values from _actual_ operations (not from speculation) and then memoiz=
ing them.
>
> The attached patchset tries to be very simple, but in my practical expe=
rience it is a very effective practical solution.
>
> When requested, I can post the mathematical theory behind the patch, or=
 I could give a presentation at some of the next conferences if I would b=
e invited (or better give a practical explanation instead). But probably =
nobody on these lists wants to deal with any theories.

Hi Thomas,

I am very interested in the theory behind your patch. Do you mind sharing=
 it? Is there
any required math background before reading it? Is there any related pape=
rs/articles I could
also read?

Thanks.

--
Best Regards
Yan Zi

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