linux-kernel - Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG

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Message-ID: <Pine.LNX.4.64.0702201041340.14643@schroedinger.engr.sgi.com>
Date:	Tue, 20 Feb 2007 10:45:55 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Max Krasnyansky <maxk@...lcomm.com>
cc:	Oleg Nesterov <oleg@...sign.ru>, Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Gautham shenoy <ego@...ibm.com>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org
Subject: Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG_CPU problems

On Tue, 20 Feb 2007, Max Krasnyansky wrote:

> > > Well seems that we have a set of unresolved issues with workqueues and cpu
> > > hotplug.
> 
> How about storing 'cpu' explicitly in the work queue instead of relying on the
> smp_processor_id() and friends ? That way there is no ambiguity when
> threads/timers get
> moved around.

The slab functionality is designed to work on the processor with the 
queue. These tricks will only cause more trouble in the future. The 
cache_reaper needs to be either disabled or run on the right processor. It 
should never run on the wrong processor.

The cache_reaper() is of no importance to hotplug. You just need to make 
sure that it is not in the way (disable it and if its running wait 
until the cache_reaper has finished).

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