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Date:	Fri, 21 Mar 2014 19:49:14 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Dilger, Andreas" <andreas.dilger@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Peng Tao <bergwolf@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"Drokin, Oleg" <oleg.drokin@...el.com>
Subject: Re: [PATCH 0/2] wait: introduce WQ_FLAG_EXCLUSIVE_HEAD

On 03/21, Dilger, Andreas wrote:
>
> On 2014/03/20, 11:51 AM, "Oleg Nesterov" <oleg@...hat.com> wrote:
>
> >On 03/19, Oleg Nesterov wrote:
> >>
> >> OK, I'll try to test/cleanup/resend tomorrow.
> >
> >Cough. Still un-tested, sorry. I will test it somehow and report,
> >but I'd like to send this for review right now.
> >
> >Because I simply can't decide what the new flag should actually
> >do, so please ack/nack the semantics/naming at least.
> >
> >Changes:
> >
> >	1. I decided it would be better to change __wait_event()
> >	   to accept wait.flags right now. This looks better in
> >	   any case to me, and otherwise we need to introduce the
> >	   __wait_exclusive_enum.
> >
> >	   The change looks trivial (both actually), please tell
> >	   me if you think it doesn't deserve a separate patch.
> >
> >	2. I won't insist, but WQ_FLAG_EXCLUSIVE_HEAD can be used
> >	   without WQ_FLAG_EXCLUSIVE.
> >
> >	   Unlikely this can be useful, but it looks more natural
> >	   this way. Otherwise we need to add another check to
> >	   ensure that WQ_FLAG_EXCLUSIVE_HEAD can't come alone.
> >
> >	   However, perhaps this means the new flag needs another
> >	   name. I agree in advance with any.
>
> What about:
>
> #define WQ_FLAG_HEAD	0x02

I am fine either way ;)

But _HEAD looks a bit confusing too. This flag doesn't add at the head,
it inserts the new entry before other exclusive tasks.

> #define WQ_FLAG_EXCLUSIVE_HEAD (WQ_FLAG_HEAD | WQ_FLAG_EXCLUSIVE)
>
> That avoids having WQ_FLAG_EXCLUSIVE_HEAD not actually meaning "exclusive"?
>
> Patches look reasonable at first glance.  The second patch would need
> to be changed to handle that WQ_FLAG_EXCLUSIVE_HEAD has both bits set
> (probably just replace uses of WQ_FLAG_EXCLUSIVE_HEAD with WQ_FLAG_HEAD).

Yes, s/WQ_FLAG_EXCLUSIVE_HEAD/WQ_FLAG_HEAD/ is the only change we
need in this case.

Other than define(WQ_FLAG_EXCLUSIVE_HEAD) of course, but this flags should
only be used by ___wait_event() callers.

Peter, what do you think?

Oleg.

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