linux-kernel - Re: [RFC] Cancellable MCS spinlock rework

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Date:	Thu, 03 Jul 2014 11:34:45 -0700
From:	Jason Low <jason.low2@...com>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	torvalds@...ux-foundation.org, paulmck@...ux.vnet.ibm.com,
	mingo@...nel.org, Waiman.Long@...com, linux-kernel@...r.kernel.org,
	riel@...hat.com, akpm@...ux-foundation.org, hpa@...or.com,
	andi@...stfloor.org, James.Bottomley@...senpartnership.com,
	rostedt@...dmis.org, tim.c.chen@...ux.intel.com, aswin@...com,
	scott.norton@...com, chegu_vinod@...com
Subject: Re: [RFC] Cancellable MCS spinlock rework

On Thu, 2014-07-03 at 10:09 -0700, Davidlohr Bueso wrote:
> On Thu, 2014-07-03 at 09:31 +0200, Peter Zijlstra wrote:
> > On Wed, Jul 02, 2014 at 10:30:03AM -0700, Jason Low wrote:
> > > Would potentially reducing the size of the rw semaphore structure by 32
> > > bits (for all architectures using optimistic spinning) be a nice
> > > benefit?
> > 
> > Possibly, although I had a look at the mutex structure and we didn't
> > have a hole to place it in, unlike what you found with the rwsem.
> 
> Yeah, and currently struct rw_semaphore is the largest lock we have in
> the kernel. Shaving off space is definitely welcome.

Right, especially if it could help things like xfs inode.

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