linux-kernel - Re: [patch 05/11] syslets: core code

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Message-ID: <20070214091348.GB4665@2ka.mipt.ru>
Date:	Wed, 14 Feb 2007 12:13:48 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 05/11] syslets: core code

On Tue, Feb 13, 2007 at 11:41:31PM +0100, Ingo Molnar (mingo@...e.hu) wrote:
> > Then limit it to a single page and use gup
> 
> 1024 (512 on 64-bit) is alot but not ALOT. It is also certainly not 
> ALOOOOT :-) Really, people will want to have more than 512 
> disks/spindles in the same box. I have used such a beast myself. For Tux 
> workloads and benchmarks we had parallelism levels of millions of 
> pending requests (!) on a single system - networking, socket limits, 
> disk IO combined with thousands of clients do create such scenarios. I 
> really think that such 'pinned pages' are a pretty natural fit for 
> sys_mlock() and RLIMIT_MEMLOCK, and since the kernel side is careful to 
> use the _inatomic() uaccess methods, it's safe (and fast) as well.

This will end up badly - I used the same approach in the early kevent
days and was proven to have swapable memory for the ring. I think it
would be much better to have userspace allocated ring and use
copy_to_user() there.

Btw, as a bit of advertisement, the whole completion part can be done
through kevent which already has ring buffer, queue operations and
non-racy updates... :)

> 	Ingo

-- 
	Evgeniy Polyakov
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