From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: Avoiding the dentry d_lock on final dput(), part deux: transactional memory Date: Tue, 1 Oct 2013 05:16:54 -0700 Message-ID: <20131001121654.GX19582@linux.vnet.ibm.com> References: <1380581522.6396.20.camel@pasglop> <23118.1380587771@ale.ozlabs.ibm.com> <1380593103.6396.38.camel@pasglop> <20131001031356.GP19582@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Benjamin Herrenschmidt , Linus Torvalds , Ingo Molnar , Peter Zijlstra , Waiman Long , "Chandramouleeswaran, Aswin" , "Norton, Scott J" , George Spelvin , Linux Kernel Mailing List , linux-fsdevel , ppc-dev To: Michael Neuling Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Oct 01, 2013 at 02:52:28PM +1000, Michael Neuling wrote: > >> Well we don't have to, I think Mikey wasn't totally clear about that > >> "making all registers volatile" business :-) This is just something we > >> need to handle in assembly if we are going to reclaim the suspended > >> transaction. > > Yeah, sorry. The slow path with all registers as volatile is only > needed if we get pre-empted during the transaction. > > >> > >> So basically, what we need is something along the lines of > >> enable_kernel_tm() which checks if there's a suspended user transaction > >> and if yes, kills/reclaims it. > >> > >> Then we also need to handle in our interrupt handlers that we have an > >> active/suspended transaction from a kernel state, which we don't deal > >> with at this point, and do whatever has to be done to kill it... we > >> might get away with something simple if we can state that we only allow > >> kernel transactions at task level and not from interrupt/softirq > >> contexts, at least initially. > > > > Call me a coward, but this is starting to sound a bit scary. ;-) > > We are just wanting to prototype it for now to see if we could make it > go faster. If it's worth it, then we'd consider the additional > complexity this would bring. > > I don't think it'll be that bad, but I'd certainly want to make sure > it's worth it before trying :-) OK, fair point. ;-) Thanx, Paul