linux-kernel - "mm: use early_pfn_to_nid in page_ext_init" broken on some configurations?

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Message-ID: <20170630141847.GN22917@dhcp22.suse.cz>
Date:   Fri, 30 Jun 2017 16:18:47 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.shi@...aro.org>
Cc:     Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: "mm: use early_pfn_to_nid in page_ext_init" broken on some
 configurations?

fe53ca54270a ("mm: use early_pfn_to_nid in page_ext_init") seem
to silently depend on CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID resp.
CONFIG_HAVE_MEMBLOCK_NODE_MAP. early_pfn_to_nid is returning zero with
!defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID) && !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP)
I am not sure how widely is this used but such a code is tricky. I see
how catching early allocations during defered initialization might be
useful but a subtly broken code sounds like a problem to me.  So is
fe53ca54270a worth this or we should revert it?
-- 
Michal Hocko
SUSE Labs