linux-kernel - Re: [PATCH 05/10] mm, page_alloc: Remove unnecessary updating of GFP flags during normal operation

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Message-ID: <20150728134712.GB19282@twins.programming.kicks-ass.net>
Date:	Tue, 28 Jul 2015 15:47:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Mel Gorman <mgorman@...e.com>, Linux-MM <linux-mm@...ck.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	Pintu Kumar <pintu.k@...sung.com>,
	Xishi Qiu <qiuxishi@...wei.com>, Gioh Kim <gioh.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH 05/10] mm, page_alloc: Remove unnecessary updating of GFP
 flags during normal operation

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@...radead.org
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