linux-kernel - Re: [PATCH] Introduce down

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Message-Id: <20080521011926.18bf8e81.akpm@linux-foundation.org>
Date:	Wed, 21 May 2008 01:19:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH] Introduce down_nowait()

On Wed, 21 May 2008 04:04:53 -0400 Christoph Hellwig <hch@...radead.org> wrote:

> On Tue, May 20, 2008 at 11:29:03PM -0700, Andrew Morton wrote:
> > Actually, I don't thing down_nowait() is a terribly good name, because it
> > doesn't tell the reader anything about what to expect from the return
> > value.  Does a non-zero return mean that down_wait() acquired the lock,
> > or does it not?  Something like down_try() would be better, because if
> > it returns 1 we can say "ah, the trying succeeded".
> 
> Actually, it does,

No it doesn't.  If anything, a "true" return from something called
"down_nowait()" means "I didn't wait!".  Or something.

> and the kerneldoc comment explains it in every detail
> for those who need to read it up.

Shouldn't be necessary to look it up.  By that argument we could
call it eat_at_joes() and sell the advertising space.

>  Then again semaphores and on their
> way out, and I really hate the kind of churn this thing introduces at
> this moment.  Please let all the semaphore to completion/mutex/other
> construct change settle for a while, and with a little chance this gem
> will just go away entirely.

Well, we can walk and chew gum at the same time.

The number of down_trylocks in rc3 is 51 and the number of
down_trylocks and down_nowaits in -mm is 47.  So progress is pretty
glacial.

<wonders why -mm still has seven down_trlyocks>

<oh>

./kernel/semaphore.c
./kernel/mutex.c
./include/linux/semaphore.h

Anyway, yes, I agree that the whole effort is a bit dubious and that
the time could be better directed to semaphore eliminations.
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