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Date: Mon, 28 Jan 2013 13:48:23 -0800 From: Kent Overstreet <koverstreet@...gle.com> To: Tejun Heo <tj@...nel.org> Cc: Oleg Nesterov <oleg@...hat.com>, srivatsa.bhat@...ux.vnet.ibm.com, rusty@...tcorp.com.au, linux-kernel@...r.kernel.org Subject: Re: [PATCH] generic dynamic per cpu refcounting On Mon, Jan 28, 2013 at 01:36:22PM -0800, Tejun Heo wrote: > On Mon, Jan 28, 2013 at 01:28:14PM -0800, Tejun Heo wrote: > > But at that point, the operation is already global, so there gotta be > > a lighter way to synchronize stuff than going through full grace > > period. ie. You can add a bias value before marking dead so that the > > counter never reaches zero before all percpu counters are collected > > and then unbias it right before putting the base ref, that way the > > only way you can hit zero ref is all refs are actually zero. > > Note that I'm saying that there's no need to distinguish between dying > and dead. Yeah I got that, I _think_ that makes me like the idea. > The only thing percpu part should care about it whether > percpu is on or off. We need a full grace period to turn off percpu > operations of any type but that should be the only case where full > grace period is necessary. The rest should be synchronizable via the > usual global synchronization. We probably can just test percpu > variable against NULL and forget about the encoded state numbers. Can't quite do that because initially, we use that variable for a timestamp and when we're shutting down we don't want percpu_ref_get() allocating percpu counters again. You'll probably use that as an argument against dynamic allocation :P -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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