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

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Date:	Sat, 2 Jan 2010 14:21:36 +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 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.

Am I missing anything?
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