mm/memory_hotplug: inline __offline_pages() into offline_pages()

Patch series "mm/memory_hotplug: online_pages()/offline_pages() cleanups", v2.

These are a bunch of cleanups for online_pages()/offline_pages() and
related code, mostly getting rid of memory hole handling that is no longer
necessary.  There is only a single walk_system_ram_range() call left in
offline_pages(), to make sure we don't have any memory holes.  I had some
of these patches lying around for a longer time but didn't have time to
polish them.

In addition, the last patch marks all pageblocks of memory to get onlined
MIGRATE_ISOLATE, so pages that have just been exposed to the buddy cannot
get allocated before onlining is complete.  Once heavy lifting is done,
the pageblocks are set to MIGRATE_MOVABLE, such that allocations are
possible.

I played with DIMMs and virtio-mem on x86-64 and didn't spot any
surprises.  I verified that the numer of isolated pageblocks is correctly
handled when onlining/offlining.

This patch (of 10):

There is only a single user, offline_pages(). Let's inline, to make
it look more similar to online_pages().
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Charan Teja Reddy <charante@codeaurora.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Link: https://lkml.kernel.org/r/20200819175957.28465-1-david@redhat.com
Link: https://lkml.kernel.org/r/20200819175957.28465-2-david@redhat.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -1484,11 +1484,10 @@ static int count_system_ram_pages_cb(unsigned long start_pfn,
 	return 0;
 }
 
-static int __ref __offline_pages(unsigned long start_pfn,
-		  unsigned long end_pfn)
+int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 {
-	unsigned long pfn, nr_pages = 0;
-	unsigned long offlined_pages = 0;
+	const unsigned long end_pfn = start_pfn + nr_pages;
+	unsigned long pfn, system_ram_pages = 0, offlined_pages = 0;
 	int ret, node, nr_isolate_pageblock;
 	unsigned long flags;
 	struct zone *zone;
@@ -1505,9 +1504,9 @@ static int __ref __offline_pages(unsigned long start_pfn,
 	 * memory holes PG_reserved, don't need pfn_valid() checks, and can
 	 * avoid using walk_system_ram_range() later.
 	 */
-	walk_system_ram_range(start_pfn, end_pfn - start_pfn, &nr_pages,
+	walk_system_ram_range(start_pfn, nr_pages, &system_ram_pages,
 			      count_system_ram_pages_cb);
-	if (nr_pages != end_pfn - start_pfn) {
+	if (system_ram_pages != nr_pages) {
 		ret = -EINVAL;
 		reason = "memory holes";
 		goto failed_removal;
@@ -1656,11 +1655,6 @@ static int __ref __offline_pages(unsigned long start_pfn,
 	return ret;
 }
 
-int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
-{
-	return __offline_pages(start_pfn, start_pfn + nr_pages);
-}
-
 static int check_memblock_offlined_cb(struct memory_block *mem, void *arg)
 {
 	int ret = !is_memblock_offlined(mem);