linux-kernel - Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

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Message-ID: <4BD599A7.6090202@redhat.com>
Date:	Mon, 26 Apr 2010 16:48:23 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
	hugh.dickins@...cali.co.uk, ngupta@...are.org, JBeulich@...ell.com,
	chris.mason@...cle.com, kurt.hackel@...cle.com,
	dave.mccracken@...cle.com, npiggin@...e.de,
	akpm@...ux-foundation.org, riel@...hat.com
Subject: Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

On 04/26/2010 03:45 PM, Dan Magenheimer wrote:
>> dma engines are present on commodity hardware now:
>>
>> http://en.wikipedia.org/wiki/I/O_Acceleration_Technology
>>
>> I don't know if consumer machines have them, but servers certainly do.
>> modprobe ioatdma.
>>      
> They don't seem to have gained much ground in the FIVE YEARS
> since the patch was first posted to Linux, have they?
>    

Why do you say this?  Servers have them and AFAIK networking uses them.  
There are other uses of the API in the code, but I don't know how much 
of this is for bulk copies.

> Maybe it's because memory-to-memory copy using a CPU
> is so fast (especially for page-ish quantities of data)
> and is a small percentage of CPU utilization these days?
>    

Copies take a small percentage of cpu because a lot of care goes into 
avoiding them, or placing them near the place where the copy is used.  
They certainly show up in high speed networking.

A page-sized copy is small, but many of them will be expensive.

-- 
error compiling committee.c: too many arguments to function

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