mm,memory_hotplug: drop unneeded locking

Currently, memory-hotplug code takes zone's span_writelock and pgdat's
resize_lock when resizing the node/zone's spanned pages via
{move_pfn_range_to_zone(),remove_pfn_range_from_zone()} and when resizing
node and zone's present pages via adjust_present_page_count().

These locks are also taken during the initialization of the system at boot
time, where it protects parallel struct page initialization, but they
should not really be needed in memory-hotplug where all operations are a)
synchronized on device level and b) serialized by the mem_hotplug_lock
lock.

Link: https://lkml.kernel.org/r/20210531093958.15021-1-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 82aac2e2a0d4660ce6efcc921209bf61df4e0ddc..ea1ab14e90f112e16d7855cf5c40ece59167f174 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -329,7 +329,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
        unsigned long pfn;
        int nid = zone_to_nid(zone);
 
-       zone_span_writelock(zone);
        if (zone->zone_start_pfn == start_pfn) {
                /*
                 * If the section is smallest section in the zone, it need
@@ -362,7 +361,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
                        zone->spanned_pages = 0;
                }
        }
-       zone_span_writeunlock(zone);
 }
 
 static void update_pgdat_span(struct pglist_data *pgdat)
@@ -424,10 +422,8 @@ void __ref remove_pfn_range_from_zone(struct zone *zone,
 
        clear_zone_contiguous(zone);
 
-       pgdat_resize_lock(zone->zone_pgdat, &flags);
        shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
        update_pgdat_span(pgdat);
-       pgdat_resize_unlock(zone->zone_pgdat, &flags);
 
        set_zone_contiguous(zone);
 }
@@ -638,15 +634,10 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
 
        clear_zone_contiguous(zone);
 
-       /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */
-       pgdat_resize_lock(pgdat, &flags);
-       zone_span_writelock(zone);
        if (zone_is_empty(zone))
                init_currently_empty_zone(zone, start_pfn, nr_pages);
        resize_zone_range(zone, start_pfn, nr_pages);
-       zone_span_writeunlock(zone);
        resize_pgdat_range(pgdat, start_pfn, nr_pages);
-       pgdat_resize_unlock(pgdat, &flags);
 
        /*
         * Subsection population requires care in pfn_to_online_page().
@@ -739,9 +730,7 @@ void adjust_present_page_count(struct zone *zone, long nr_pages)
        unsigned long flags;
 
        zone->present_pages += nr_pages;
-       pgdat_resize_lock(zone->zone_pgdat, &flags);
        zone->zone_pgdat->node_present_pages += nr_pages;
-       pgdat_resize_unlock(zone->zone_pgdat, &flags);
 }
 
 int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,