memremap: replace the altmap_valid field with a PGMAP_ALTMAP_VALID flag

Add a flags field to struct dev_pagemap to replace the altmap_valid
boolean to be a little more extensible.  Also add a pgmap_altmap() helper
to find the optional altmap and clean up the code using the altmap using
it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d66bc8abe0af..17a39d40a556 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5853,6 +5853,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 {
         unsigned long pfn, end_pfn = start_pfn + size;
         struct pglist_data *pgdat = zone->zone_pgdat;
+        struct vmem_altmap *altmap = pgmap_altmap(pgmap);
         unsigned long zone_idx = zone_idx(zone);
         unsigned long start = jiffies;
         int nid = pgdat->node_id;
@@ -5865,9 +5866,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
          * of the pages reserved for the memmap, so we can just jump to
          * the end of that region and start processing the device pages.
          */
-        if (pgmap->altmap_valid) {
-                struct vmem_altmap *altmap = &pgmap->altmap;
-
+        if (altmap) {
                 start_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
                 size = end_pfn - start_pfn;
         }