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

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Date:	Sat, 2 Jan 2010 22:29:41 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
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

2010/1/2 Peter Zijlstra <peterz@...radead.org>:
> 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.

Umm, probably I haven't catch your mention. currently kswapd never
call __zone_reclaim() because
kswapd has PF_MEMALLOC and PF_MEMALLOC prevent to call __zone_reclaim
(see zone_reclaim()).

When recursive annotation occur?
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