linux-kernel - Re: Linux 3.19-rc3

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Message-ID: <20150106130317.GX29390@twins.programming.kicks-ass.net>
Date:	Tue, 6 Jan 2015 14:03:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kent Overstreet <kmo@...erainc.com>
Cc:	Sedat Dilek <sedat.dilek@...il.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Chris Mason <clm@...com>
Subject: Re: Linux 3.19-rc3

On Tue, Jan 06, 2015 at 04:43:13AM -0800, Kent Overstreet wrote:
> It might make the most sense to cook up something new, stealing some of the
> closure code but using standard the wait_queue_head_t - having a single standard
> waitlist type is definitely a good thing, and unfortunately I don't think it'd
> be a good idea to convert closures to wait_queue_head_t mainly because of the
> memory usage.
> 
> I will note that one thing that has been immensely useful with closures is the
> ability to pass a closure around - think of it as a "wait object" - to some code
> that may end up waiting on something, but you don't want to itself sleep, and
> then the caller can closure_sync() or continue_at() or whatever it wants (or use
> the same closure for waiting on multiple things, e.g. where we wait on writing
> the two new btree nodes after a split).
> 
> Think of it a souped up completion.

Yeah I got that aspect. I'm still trying to get my head around how the
wait_event bit would be a natural match though ;-)

Let me stew a bit on that.

That said, the RT people want a simple waitqueue, one that has
deterministic behaviour. This is only possibly by removing some of the
more obscure waitqueue features and thus also results in a slimmer
structure.

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