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From: Michal Hocko <mhocko@kernel.org>
To: Yang Shi <yang.shi@linaro.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: "mm: use early_pfn_to_nid in page_ext_init" broken on some configurations?
Date: Fri, 30 Jun 2017 17:42:24 +0200	[thread overview]
Message-ID: <20170630154224.GA9714@dhcp22.suse.cz> (raw)
In-Reply-To: <20170630141847.GN22917@dhcp22.suse.cz>

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

WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org>
To: Yang Shi <yang.shi@linaro.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: "mm: use early_pfn_to_nid in page_ext_init" broken on some configurations?
Date: Fri, 30 Jun 2017 17:42:24 +0200	[thread overview]
Message-ID: <20170630154224.GA9714@dhcp22.suse.cz> (raw)
In-Reply-To: <20170630141847.GN22917@dhcp22.suse.cz>

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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  reply	other threads:[~2017-06-30 15:42 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-30 14:18 "mm: use early_pfn_to_nid in page_ext_init" broken on some configurations? Michal Hocko
2017-06-30 14:18 ` Michal Hocko
2017-06-30 15:42 ` Michal Hocko [this message]
2017-06-30 15:42   ` Michal Hocko
2017-06-30 15:44   ` Michal Hocko
2017-06-30 15:44     ` Michal Hocko
2017-07-04  5:11     ` Joonsoo Kim
2017-07-04  5:11       ` Joonsoo Kim
2017-07-04  6:51       ` Michal Hocko
2017-07-04  6:51         ` Michal Hocko
2017-07-03 11:48 ` Vlastimil Babka
2017-07-03 11:48   ` Vlastimil Babka
2017-07-03 14:18   ` Vlastimil Babka
2017-07-03 14:18     ` Vlastimil Babka
2017-07-04  5:23     ` Joonsoo Kim
2017-07-04  5:23       ` Joonsoo Kim
2017-07-04  9:39       ` Vlastimil Babka
2017-07-04  9:39         ` Vlastimil Babka
2017-07-04 10:53         ` Michal Hocko
2017-07-04 10:53           ` Michal Hocko
2017-07-04  5:17   ` Joonsoo Kim
2017-07-04  5:17     ` Joonsoo Kim
2017-07-07 12:00     ` Vlastimil Babka
2017-07-07 12:00       ` Vlastimil Babka
2017-07-14  9:13       ` Michal Hocko
2017-07-14  9:13         ` Michal Hocko
2017-07-14  9:34         ` Vlastimil Babka
2017-07-14  9:34           ` Vlastimil Babka
2017-07-14 11:35           ` Michal Hocko
2017-07-14 11:35             ` Michal Hocko

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