mm: free_area_init: allow defining max_zone_pfn in descending order

Some architectures (e.g.  ARC) have the ZONE_HIGHMEM zone below the
ZONE_NORMAL.  Allowing free_area_init() parse max_zone_pfn array even it
is sorted in descending order allows using free_area_init() on such
architectures.

Add top -> down traversal of max_zone_pfn array in free_area_init() and
use the latter in ARC node/zone initialization.

[rppt@kernel.org: ARC fix]
  Link: http://lkml.kernel.org/r/20200504153901.GM14260@kernel.org
[rppt@linux.ibm.com: arc: free_area_init(): take into account PAE40 mode]
  Link: http://lkml.kernel.org/r/20200507205900.GH683243@linux.ibm.com
[akpm@linux-foundation.org: declare arch_has_descending_max_zone_pfns()]
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Hoan Tran <hoan@os.amperecomputing.com>	[arm64]
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Cc: Guan Xuetao <gxt@pku.edu.cn>
Cc: Guo Ren <guoren@kernel.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Rich Felker <dalias@libc.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Guenter Roeck <linux@roeck-us.net>
Link: http://lkml.kernel.org/r/20200412194859.12663-18-rppt@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 21 insertions, 5 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1f7eff7120d7..36d93c73f2bb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7408,6 +7408,15 @@ static void check_for_memory(pg_data_t *pgdat, int nid)
 	}
 }
 
+/*
+ * Some architecturs, e.g. ARC may have ZONE_HIGHMEM below ZONE_NORMAL. For
+ * such cases we allow max_zone_pfn sorted in the descending order
+ */
+bool __weak arch_has_descending_max_zone_pfns(void)
+{
+	return false;
+}
+
 /**
  * free_area_init - Initialise all pg_data_t and zone data
  * @max_zone_pfn: an array of max PFNs for each zone
@@ -7424,7 +7433,8 @@ static void check_for_memory(pg_data_t *pgdat, int nid)
 void __init free_area_init(unsigned long *max_zone_pfn)
 {
 	unsigned long start_pfn, end_pfn;
-	int i, nid;
+	int i, nid, zone;
+	bool descending;
 
 	/* Record where the zone boundaries are */
 	memset(arch_zone_lowest_possible_pfn, 0,
@@ -7433,14 +7443,20 @@ void __init free_area_init(unsigned long *max_zone_pfn)
 				sizeof(arch_zone_highest_possible_pfn));
 
 	start_pfn = find_min_pfn_with_active_regions();
+	descending = arch_has_descending_max_zone_pfns();
 
 	for (i = 0; i < MAX_NR_ZONES; i++) {
-		if (i == ZONE_MOVABLE)
+		if (descending)
+			zone = MAX_NR_ZONES - i - 1;
+		else
+			zone = i;
+
+		if (zone == ZONE_MOVABLE)
 			continue;
 
-		end_pfn = max(max_zone_pfn[i], start_pfn);
-		arch_zone_lowest_possible_pfn[i] = start_pfn;
-		arch_zone_highest_possible_pfn[i] = end_pfn;
+		end_pfn = max(max_zone_pfn[zone], start_pfn);
+		arch_zone_lowest_possible_pfn[zone] = start_pfn;
+		arch_zone_highest_possible_pfn[zone] = end_pfn;
 
 		start_pfn = end_pfn;
 	}