[RFC] Move the memory_notifier out of the memory_hotplug lock

From: Nathan Zimmer
Date: Wed Feb 05 2014 - 11:29:18 EST


There are a few spots where we call memory_notifier. This doesn't need to be
done under lock since memory_notify is just a blocking_notifier_call_chain
with it's own locking mechanism.

This RFC is a follow on to the one I submitted earlier.
(move register_memory_resource out of the lock_memory_hotplug, commit ac13c46)
Most of our time is being spend under the memory hotplug lock in particular
online_pages() so it makes sense to move out everything that can be easily
moved out.

However perf pointed me to a spot to work on, setup_zone_migrate_reserve.
In fact most of the time is spent there. Since that is going to require
more reading and time I will start by whittling out some easy pieces.

cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
cc: Tang Chen <tangchen@xxxxxxxxxxxxxx>
cc: Wen Congyang <wency@xxxxxxxxxxxxxx>
cc: Toshi Kani <toshi.kani@xxxxxx>
cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
cc: Xishi Qiu <qiuxishi@xxxxxxxxxx>
cc: Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx>
cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
cc: David Rientjes <rientjes@xxxxxxxxxx>
cc: Jiang Liu <liuj97@xxxxxxxxx>
Cc: Hedi Berriche <hedi@xxxxxxx>
Cc: Mike Travis <travis@xxxxxxx>
linux-mm@xxxxxxxxx (open list:MEMORY MANAGEMENT)
linux-kernel@xxxxxxxxxxxxxxx (open list)

---
mm/memory_hotplug.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 62a0cd1..a3cbd14 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -985,12 +985,12 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
if (need_zonelists_rebuild)
zone_pcp_reset(zone);
mutex_unlock(&zonelists_mutex);
+ unlock_memory_hotplug();
printk(KERN_DEBUG "online_pages [mem %#010llx-%#010llx] failed\n",
(unsigned long long) pfn << PAGE_SHIFT,
(((unsigned long long) pfn + nr_pages)
<< PAGE_SHIFT) - 1);
memory_notify(MEM_CANCEL_ONLINE, &arg);
- unlock_memory_hotplug();
return ret;
}

@@ -1016,9 +1016,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ

writeback_set_ratelimit();

+ unlock_memory_hotplug();
+
if (onlined_pages)
memory_notify(MEM_ONLINE, &arg);
- unlock_memory_hotplug();

return 0;
}
@@ -1601,8 +1602,8 @@ repeat:
vm_total_pages = nr_free_pagecache_pages();
writeback_set_ratelimit();

- memory_notify(MEM_OFFLINE, &arg);
unlock_memory_hotplug();
+ memory_notify(MEM_OFFLINE, &arg);
return 0;

failed_removal:
--
1.8.2.1

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