linux-kernel - Re: [RFC PATCH 0/7] evacuate struct page from the block layer

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Message-ID: <550C8E82.2020309@youngman.org.uk>
Date:	Fri, 20 Mar 2015 21:17:54 +0000
From:	Wols Lists <antlists@...ngman.org.uk>
To:	Matthew Wilcox <willy@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	axboe@...nel.dk, linux-nvdimm@...1.01.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-raid@...r.kernel.org, mgorman@...e.de, hch@...radead.org,
	linux-fsdevel@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [RFC PATCH 0/7] evacuate struct page from the block layer

On 20/03/15 20:31, Matthew Wilcox wrote:
> Ah!  I've looked at that a couple of times as well.  I asked our database
> performance team what impact freeing up the memmap would have on their
> performance.  They told me that doubling the amount of memory generally
> resulted in approximately a 40% performance improvement.  So freeing up
> 1.5% additional memory would result in about 0.6% performance improvement,
> which I thought was probably too small a return on investment to justify
> turning memmap into a two-level data structure.

Don't get me started on databases! This is very much a relational
problem, other databases don't suffer like this.

(imho relational theory is totally inappropriate for an engineering
problem, like designing a database engine ...)

Cheers,
Wol
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