[PATCH] um/mm: get max_low_pfn from memblock

[Wei Yang <richard.weiyang@gmail.com>]

Current calculation of max_low_pfn is introduced in commit af84eab20891
("[PATCH] uml: fix LVM crash"). It is intended to set max_low_pfn to the
same value as max_pfn.

But I am not sure why the max_pfn is set to totalram_pages, which
represents the number of usable pages in system instead of an absolute
page frame number. (The change history stops there.)

While we can get the maximum page frame number from memblock, this looks
more reasonable than setting to totalram_pages.

Also this would help changing totalram_pages accounting, since we plan
to move the accounting into __free_pages_core(). With this change,
totalram_pages may not represent the total usable pages at this point,
since some pages would be deferred initialized.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Jason Lunz <lunz@falooley.org>
CC: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Alasdair G Kergon <agk@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Mike Rapoport (IBM) <rppt@kernel.org>
CC: David Hildenbrand <david@redhat.com>

---
A simple UML bootup test looks good.
---
 arch/um/kernel/mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index ca91accd64fc..ca682879e28f 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -73,7 +73,7 @@ void __init mem_init(void)
 
 	/* this will put all low memory onto the freelists */
 	memblock_free_all();
-	max_low_pfn = totalram_pages();
+	max_low_pfn = PFN_DOWN(memblock_end_of_DRAM());
 	max_pfn = max_low_pfn;
 	kmalloc_ok = 1;
 }
-- 
2.34.1