linux-kernel - Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

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Date:	Fri, 16 Jul 2010 21:32:00 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <rostedt@...tedt.homelinux.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@....de>, Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>, akpm@...l.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

On 07/16/2010 09:22 PM, Mathieu Desnoyers wrote:
>
>> There aren't that many processes at this time (or there shouldn't be,
>> don't know how fork-happy udev is at this stage), so the sync should be
>> pretty fast.  In any case, we can sync only modules that contain NMI
>> handlers.
>>      
> USB hotplug is a use-case happening randomly after the system is well there and
> running; I'm afraid this does not fit in your module loading expectations. It
> triggers tons of events, many of these actually load modules.
>    

How long would vmalloc_sync_all take with a few thousand mm_struct take?

We share the pmds, yes?  So it's a few thousand memory accesses.  The 
direct impact is probably negligible, compared to actually loading the 
module from disk.  All we need is to make sure the locking doesn't slow 
down unrelated stuff.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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