mm, memory_hotplug: get rid of zonelists_mutex
zonelists_mutex was introduced by commit 4eaf3f64397c ("mem-hotplug: fix
potential race while building zonelist for new populated zone") to
protect zonelist building from races. This is no longer needed though
because both memory online and offline are fully serialized. New users
have grown since then.
Notably setup_per_zone_wmarks wants to prevent from races between memory
hotplug, khugepaged setup and manual min_free_kbytes update via sysctl
(see cfd3da1e49bb ("mm: Serialize access to min_free_kbytes"). Let's
add a private lock for that purpose. This will not prevent from seeing
halfway through memory hotplug operation but that shouldn't be a big
deal becuse memory hotplug will update watermarks explicitly so we will
eventually get a full picture. The lock just makes sure we won't race
when updating watermarks leading to weird results.
Also __build_all_zonelists manipulates global data so add a private lock
for it as well. This doesn't seem to be necessary today but it is more
robust to have a lock there.
While we are at it make sure we document that memory online/offline
depends on a full serialization either via mem_hotplug_begin() or
device_lock.
Link: http://lkml.kernel.org/r/20170721143915.14161-9-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Haicheng Li <haicheng.li@linux.intel.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2f0c7eb..73bf17d 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -897,7 +897,7 @@
return zone;
}
-/* Must be protected by mem_hotplug_begin() */
+/* Must be protected by mem_hotplug_begin() or a device_lock */
int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type)
{
unsigned long flags;
@@ -926,7 +926,6 @@
* This means the page allocator ignores this zone.
* So, zonelist must be updated after online.
*/
- mutex_lock(&zonelists_mutex);
if (!populated_zone(zone)) {
need_zonelists_rebuild = 1;
setup_zone_pageset(zone);
@@ -937,7 +936,6 @@
if (ret) {
if (need_zonelists_rebuild)
zone_pcp_reset(zone);
- mutex_unlock(&zonelists_mutex);
goto failed_addition;
}
@@ -955,8 +953,6 @@
zone_pcp_update(zone);
}
- mutex_unlock(&zonelists_mutex);
-
init_per_zone_wmark_min();
if (onlined_pages) {
@@ -1027,9 +1023,7 @@
* The node we allocated has no zone fallback lists. For avoiding
* to access not-initialized zonelist, build here.
*/
- mutex_lock(&zonelists_mutex);
build_all_zonelists(pgdat);
- mutex_unlock(&zonelists_mutex);
/*
* zone->managed_pages is set to an approximate value in
@@ -1696,9 +1690,7 @@
if (!populated_zone(zone)) {
zone_pcp_reset(zone);
- mutex_lock(&zonelists_mutex);
build_all_zonelists(NULL);
- mutex_unlock(&zonelists_mutex);
} else
zone_pcp_update(zone);
@@ -1724,7 +1716,7 @@
return ret;
}
-/* Must be protected by mem_hotplug_begin() */
+/* Must be protected by mem_hotplug_begin() or a device_lock */
int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
{
return __offline_pages(start_pfn, start_pfn + nr_pages, 120 * HZ);