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

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Message-ID: <45DB6FC7.60502@qualcomm.com>
Date:	Tue, 20 Feb 2007 14:01:43 -0800
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Christoph Lameter <clameter@....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

Christoph Lameter wrote:
> On Tue, 20 Feb 2007, Max Krasnyansky wrote:
> 
>> I guess I kind of hijacked the thread. The second part of my first email was
>> dropped. Basically I was saying that I'm working on CPU isolation extensions.
>> Where an isolated CPU is not supposed to do much kernel work. In which case
>> you'd want to run slab cache reaper on some other CPU on behalf of the
>> isolated
>> one. Hence the proposal to explicitly pass cpu_id to the reaper. I guess now
>> that you guys fixed the hotplug case it does not help in that scenario.
> 
> A cpu must have a per cpu cache in order to do slab allocations. The 
> locking in the slab allocator depends on it.
> 
> If the isolated cpus have no need for slab allocations then you will also 
> not need to run the slab_reaper().

Ok. Sounds like disabling cache_reaper is a better option for now. Like you said
it's unlikely that slabs will grow much if that cpu is not heavily used by the
kernel.

Thanks
Max
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