Date: Tue, 28 Jul 2015 15:47:12 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.com>, Linux-MM <linux-mm@kvack.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Rik van Riel <riel@redhat.com>,
        Pintu Kumar <pintu.k@samsung.com>, Xishi Qiu <qiuxishi@huawei.com>,
        Gioh Kim <gioh.kim@lge.com>, LKML <linux-kernel@vger.kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH 05/10] mm, page_alloc: Remove unnecessary updating of GFP
 flags during normal operation
Message-ID: <20150728134712.GB19282@twins.programming.kicks-ass.net>
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 <1437379219-9160-6-git-send-email-mgorman@suse.com>
 <55B78545.8000906@suse.cz>
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On Tue, Jul 28, 2015 at 03:36:05PM +0200, Vlastimil Babka wrote:
> >+static inline gfp_t gfp_allowed_mask(gfp_t gfp_mask)
> >+{
> >+	if (static_key_false(&gfp_restricted_key))
> 
> This is where it uses static_key_false()...

> >+struct static_key gfp_restricted_key __read_mostly = STATIC_KEY_INIT_TRUE;
> 
> ... and here it's combined with STATIC_KEY_INIT_TRUE. I've suspected that
> this is not allowed, which Peter confirmed on IRC.
> 
> It's however true that the big comment at the top of
> include/linux/jump_label.h only explicitly talks about combining
> static_key_false() and static_key_true().
> 
> I'm not sure what's the correct idiom for a default-false static key which
> however has to start as true on boot (Peter said such cases do exist)...

There currently isn't one. But see the patchset I just send to address
this:

  lkml.kernel.org/r/20150728132313.164884020@infradead.org
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