linux-kernel - Re: [PATCH 0 of 4] Generic AIO by scheduling stacks

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Date:	Fri, 9 Feb 2007 16:12:45 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eric Dumazet <dada1@...mosbay.com>
cc:	Zach Brown <zach.brown@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-aio@...ck.org, Suparna Bhattacharya <suparna@...ibm.com>,
	Benjamin LaHaise <bcrl@...ck.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 0 of 4] Generic AIO by scheduling stacks

On Sat, 10 Feb 2007, Eric Dumazet wrote:
> 
> Well, I guess if the original program was mono-threaded, and syscall used
> fget_light(), we might have a problem here if the child try a close(). So you
> may have to disable fget_light() magic if async call is the originator of the
> syscall.

Yes. All the issues that I already brought up with Zach's patches are 
still there. This doesn't really change any of them. Any optimization that 
checks for "am I single-threaded" will need to be aware of pending and 
running async things.

With my patch, any _running_ async things will always be seen as normal 
clones, but the pending ones won't. So you'd need to effectively change 
anything that looks like

	if (atomic_read(&current->mm->count) == 1)
		.. do some simplified version ..

into

	if (!current->async_cookie && atomic_read(..) == 1)
		.. do the simplified thing ..

to make it safe.

I think we only do it for fget_light and some VM TLB simplification, so it 
shouldn't be a big burden to check.

Side note: the real issues still remain. The interfaces, and the 
performance testing.

		Linus
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