linux-kernel - Re: [RFC]: Support for zero-copy TCP transmit of user space data

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Message-ID: <494BDBFC.7060707@vlnb.net>
Date:	Fri, 19 Dec 2008 20:38:04 +0300
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Andi Kleen <andi@...stfloor.org>
CC:	linux-mm@...ck.org, Christoph Hellwig <hch@...radead.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	scst-devel@...ts.sourceforge.net,
	Bart Van Assche <bart.vanassche@...il.com>,
	netdev@...r.kernel.org
Subject: Re: [RFC]: Support for zero-copy TCP transmit of user space data

Andi Kleen, on 12/19/2008 02:27 PM wrote:
> Vladislav Bolkhovitin <vst@...b.net> writes:
>>  - Although usage of struct page to keep network related pointer might
>> look as a layering violation, it isn't. I wrote in
>> http://lkml.org/lkml/2008/12/15/190 why.
> 
> Sorry but extending struct page for this is really a bad idea because
> of the extreme memory overhead even when it's not used (which is a 
> problem on distribution kernels) Find some other way to store this
> information.  Even for patches with more general value it was not
> acceptable.

Sure, this is why I propose to disable that option by default in 
distribution kernels, so it would produce no harm. ISCSI-SCST can work 
in this configuration quite well too. People who need both iSCSI target 
*and* fast working user space device handlers would simply enable that 
option and rebuild the kernel. Rejecting this patch provides much worse 
alternative: those people would also have to *patch* the kernel at 
first, only then enable that option, then rebuild the kernel. (I'm 
repeating it to make sure you didn't miss this my point; it was in the 
part of my original message, which you cut out.)

Thanks,
Vlad
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