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Date: Fri, 30 Jun 2017 17:42:24 +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: Re: "mm: use early_pfn_to_nid in page_ext_init" broken on some configurations? On Fri 30-06-17 16:18:47, Michal Hocko wrote: > 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? I've dug little bit further. It seems that only s390 and ia64 select HAVE_ARCH_EARLY_PFN_TO_NID. Much more architectures enabled HAVE_MEMBLOCK_NODE_MAP though but still alpha, arc, arm, avr32, blackfin, c6x, cris, frv, h8300, hexagon, Kconfig, m32r, m68k, mn10300, nios2, openrisc, parisc, tile, um, unicore32, xtensa do not. I can only see alpha having NUMA and even that is marked BROKEN. So it seems that this is not a real problem after all. Still subtle, so I guess we want to have the following. What do you think? diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 16532fa0bb64..894697c1e6f5 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1055,6 +1055,7 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist, !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) static inline unsigned long early_pfn_to_nid(unsigned long pfn) { + BUILD_BUG_ON(!IS_ENABLED(CONFIG_NUMA)); return 0; } #endif -- Michal Hocko SUSE Labs
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