linux-kernel - Re: [PATCH -mmotm] mm/memory_hotplug: fix for CONFIG_ZONE

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Date:   Tue, 19 Jan 2021 20:12:01 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mark Brown <broonie@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Michal Hocko <mhocko@...e.cz>, mm-commits@...r.kernel.org,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH -mmotm] mm/memory_hotplug: fix for CONFIG_ZONE_DEVICE not enabled

On Tue, Jan 19, 2021 at 7:05 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>
> From: Randy Dunlap <rdunlap@...radead.org>
>
> Fix memory_hotplug.c when CONFIG_ZONE_DEVICE is not enabled.
>
> Fixes this build error:
>
> ../mm/memory_hotplug.c: In function ‘move_pfn_range_to_zone’:
> ../mm/memory_hotplug.c:772:24: error: ‘ZONE_DEVICE’ undeclared (first use in this function); did you mean ‘ZONE_MOVABLE’?
>   if (zone_idx(zone) == ZONE_DEVICE) {

Thanks Randy. Apologies for the thrash, obviously the kbuild-robot
does not include a CONFIG_ZONE_DEVICE=n.

I'd prefer to fix this without adding ifdefery in a .c file with
something like this:

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0b5c44f730b4..66ba38dae9ba 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -885,6 +885,18 @@ static inline int local_memory_node(int node_id)
{ return node_id; };
  */
 #define zone_idx(zone)         ((zone) - (zone)->zone_pgdat->node_zones)

+#ifdef CONFIG_ZONE_DEVICE
+static inline bool zone_is_zone_device(struct zone *zone)
+{
+       return zone_idx(zone) == ZONE_DEVICE;
+}
+#else
+static inline bool zone_is_zone_device(struct zone *zone)
+{
+       return false;
+}
+#endif
+
 /*
  * Returns true if a zone has pages managed by the buddy allocator.
  * All the reclaim decisions have to use this function rather than
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c78a1bef561b..710e469fb3a1 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -769,7 +769,7 @@ void __ref move_pfn_range_to_zone(struct zone
*zone, unsigned long start_pfn,
         * ZONE_DEVICE pages in an otherwise  ZONE_{NORMAL,MOVABLE}
         * section.
         */
-       if (zone_idx(zone) == ZONE_DEVICE) {
+       if (zone_is_zone_device(zone)) {
                if (!IS_ALIGNED(start_pfn, PAGES_PER_SECTION))
                        section_taint_zone_device(start_pfn);
                if (!IS_ALIGNED(start_pfn + nr_pages, PAGES_PER_SECTION))