linux-kernel - Re: [PATCH v2 0/5] Reenable might_sleep() checks for might

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Message-ID: <20150209144217.GT5029@twins.programming.kicks-ass.net>
Date:	Mon, 9 Feb 2015 15:42:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	tglx@...utronix.de, benh@...nel.crashing.org, paulus@...ba.org,
	akpm@...ux-foundation.org, heiko.carstens@...ibm.com,
	schwidefsky@...ibm.com, borntraeger@...ibm.com, mst@...hat.com,
	David.Laight@...LAB.COM, hughd@...gle.com, hocko@...e.cz
Subject: Re: [PATCH v2 0/5] Reenable might_sleep() checks for might_fault()

On Mon, Jan 12, 2015 at 03:19:11PM +0100, David Hildenbrand wrote:
> Thomas, Peter,
> 
> anything that speaks against putting the pagefault_disable counter into
> thread_info (my series) instead of task_struct (rt tree)?
> 
> IOW, what would be the right place for it?

I think we put it in task_struct because lazy; ARM seems one of the few
popular archs where current still goes through thread_info.

And that I think is the only reason to maybe use thread_info, cost of
access. The down-side of using thread_info is of course that it reduces
stack size.

In any case; I think that if you want to go do this; please consider the
route -rt took and completely separate the two, don't leave the
preempt_count_{inc,dec} remnant in pagefault_{en,dis}able() at all.

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