mm: simplify find_min_pfn_with_active_regions()

find_min_pfn_with_active_regions() calls find_min_pfn_for_node() with nid
parameter set to MAX_NUMNODES.  This makes the find_min_pfn_for_node()
traverse all memblock memory regions although the first PFN in the system
can be easily found with memblock_start_of_DRAM().

Use memblock_start_of_DRAM() in find_min_pfn_with_active_regions() and drop
now unused find_min_pfn_for_node().
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]
Cc: 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>
Link: http://lkml.kernel.org/r/20200412194859.12663-21-rppt@kernel.orgSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -7066,24 +7066,6 @@ unsigned long __init node_map_pfn_alignment(void)
 	return ~accl_mask + 1;
 }
 
-/* Find the lowest pfn for a node */
-static unsigned long __init find_min_pfn_for_node(int nid)
-{
-	unsigned long min_pfn = ULONG_MAX;
-	unsigned long start_pfn;
-	int i;
-
-	for_each_mem_pfn_range(i, nid, &start_pfn, NULL, NULL)
-		min_pfn = min(min_pfn, start_pfn);
-
-	if (min_pfn == ULONG_MAX) {
-		pr_warn("Could not find start_pfn for node %d\n", nid);
-		return 0;
-	}
-
-	return min_pfn;
-}
-
 /**
  * find_min_pfn_with_active_regions - Find the minimum PFN registered
  *
@@ -7092,7 +7074,7 @@ static unsigned long __init find_min_pfn_for_node(int nid)
  */
 unsigned long __init find_min_pfn_with_active_regions(void)
 {
-	return find_min_pfn_for_node(MAX_NUMNODES);
+	return PHYS_PFN(memblock_start_of_DRAM());
 }
 
 /*