linux-kernel - Re: [patch v3] splice: fix race with page invalidation

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Message-Id: <E1KOGT8-0000rd-0Z@pomaz-ex.szeredi.hu>
Date:	Wed, 30 Jul 2008 20:32:14 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	jens.axboe@...cle.com
CC:	miklos@...redi.hu, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, nickpiggin@...oo.com.au,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch v3] splice: fix race with page invalidation

On Wed, 30 Jul 2008, Jens Axboe wrote:
> On Wed, Jul 30 2008, Miklos Szeredi wrote:
> > On Wed, 30 Jul 2008, Linus Torvalds wrote:
> > > On Wed, 30 Jul 2008, Miklos Szeredi wrote:
> > > > 
> > > > There are no real disadvantages: splice() from a file was
> > > > originally meant to be asynchronous, but in reality it only did
> > > > that for non-readahead pages, which happen rarely.
> > > 
> > > I still don't like this. I still don't see the point, and I still
> > > think there is something fundamentally wrong elsewhere.
> 
> You snipped the part where Linus objected to dismissing the async
> nature, I fully agree with that part.
> 
> > We discussed the possible solutions with Nick, and came to the
> > conclusion, that short term (i.e. 2.6.27) this is probably the best
> > solution.
> 
> Ehm where?

http://lkml.org/lkml/2008/7/7/476

>  Nick also said that he didn't like removing the ->confirm()
> bits as they are completely related to the async nature of splice. You
> already submitted this exact patch earlier and it was nak'ed.

That's not true.  The resubmitted patch didn't remove the ->confirm()
calls, which is what Nick objected to, I think.

> > Long term sure, I have no problem with implementing async splice.
> > 
> > In fact, I may even have personal interest in looking at splice,
> > because people are asking for a zero-copy interface for fuse.
> > 
> > But that is definitely not 2.6.27, so I think you should reconsider
> > taking this patch, which is obviously correct due to its simplicity,
> > and won't cause any performance regressions either.
> 
> Then please just fix the issue, instead of removing the bits that make
> this possible.

I tried to fix it, but Nick didn't like my fix.  Ideas are of course
welcome.

Thanks,
Miklos
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