linux-kernel - Re: [RFC:Patch: 000/008](memory hotplug) rough idea of pgdat removing

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Message-ID: <4891C66A.3040302@linux-foundation.org>
Date:	Thu, 31 Jul 2008 09:04:26 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Yasunori Goto <y-goto@...fujitsu.com>
CC:	Badari Pulavarty <pbadari@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, linux-mm <linux-mm@...ck.org>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC:Patch: 000/008](memory hotplug) rough idea of pgdat removing

Yasunori Goto wrote:

> Current my idea is using RCU feature for waiting them.
> Because it is the least impact against reader's performance,
> and pgdat remover can wait finish of reader's access to pgdat
> which is removing by synchronize_sched().

The use of RCU disables preemption which has implications as to what can be done in a loop over nodes or zones. This would also potentially add more overhead to the page allocator hotpaths.


> If you have better idea, please let me know.

Use stop_machine()? The removal of a zone or node is a pretty rare event after all and it would avoid having to deal with rcu etc etc.

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