linux-kernel - Re: [PATCH] mm, lockdep: annotate reclaim context to zone reclaim too

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Date:	Sat, 02 Jan 2010 11:46:06 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] mm, lockdep: annotate reclaim context to zone reclaim
 too

On Sat, 2010-01-02 at 14:21 +0900, KOSAKI Motohiro wrote:
> 2010/1/2 Peter Zijlstra <peterz@...radead.org>:
> > On Fri, 2010-01-01 at 18:45 +0900, KOSAKI Motohiro wrote:
> >> Commit cf40bd16fd (lockdep: annotate reclaim context) introduced reclaim
> >> context annotation. But it didn't annotate zone reclaim. This patch do it.
> >
> > And yet you didn't CC anyone involved in that patch, nor explain why you
> > think it necessary, massive FAIL.
> >
> > The lockdep annotations cover all of kswapd() and direct reclaim through
> > __alloc_pages_direct_reclaim(). So why would you need an explicit
> > annotation in __zone_reclaim()?
> 
> Thanks CCing. The point is zone-reclaim doesn't use
> __alloc_pages_direct_reclaim.
> current call graph is
> 
> __alloc_pages_nodemask
>     get_page_from_freelist
>         zone_reclaim()
>     __alloc_pages_slowpath
>         __alloc_pages_direct_reclaim
>             try_to_free_pages
> 
> Actually, if zone_reclaim_mode=1, VM never call
> __alloc_pages_direct_reclaim in usual VM pressure.
> Thus I think zone-reclaim should be annotated explicitly too.
> I know almost user don't use zone reclaim mode. but explicit
> annotation doesn't have any demerit, I think.

Just be aware that the annotation isn't recursive, I'd have to trace all
calls to __zone_reclaim, but if kswapd were ever to call it you'd just
wrecked things by getting lockdep_clear_current_reclaim_state() called.

So just make sure you don't shorten the existing notations by adding it
here. Other than that it seems ok.

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