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Date:   Sun, 5 Nov 2017 08:45:09 +0100
From:   Michal Hocko <>
Cc:     Peter Zijlstra <>,
        Thomas Gleixner <>,
        Johannes Weiner <>,
        Mel Gorman <>, Tejun Heo <>,
        LKML <>
Subject: [PATCH -v2] mm: drop hotplug lock from lru_add_drain_all

Here is v2 which drops the IRQ disabling in the hotplug callback and
fixes the compile breakage. The patch 1 is wrong as pointed out by Hugh,
but this one alone should help already.
>From 53d3003635bfa619745048aa4b70ca62f714960d Mon Sep 17 00:00:00 2001
From: Michal Hocko <>
Date: Thu, 2 Nov 2017 10:19:17 +0100
Subject: [PATCH] mm: drop hotplug lock from lru_add_drain_all

Pulling cpu hotplug locks inside the mm core function like
lru_add_drain_all just asks for problems and the recent lockdep splat
[1] just proves this. While the usage in that particular case might
be wrong we should prevent from locking as lru_add_drain_all is used
at many places. It seems that this is not all that hard to achieve

We have done the same thing for drain_all_pages which is analogous by
a459eeb7b852 ("mm, page_alloc: do not depend on cpu hotplug locks inside
the allocator"). All we have to care about is to handle
      - the work item might be executed on a different cpu in worker from
        unbound pool so it doesn't run on pinned on the cpu

      - we have to make sure that we do not race with page_alloc_cpu_dead
        calling lru_add_drain_cpu

the first part is already handled because the worker calls lru_add_drain
which disables preemption when calling lru_add_drain_cpu on the local
cpu it is draining. The later is true because page_alloc_cpu_dead
is called on the controlling CPU after the hotplugged CPU vanished


Signed-off-by: Michal Hocko <>
 include/linux/swap.h | 1 -
 mm/memory_hotplug.c  | 2 +-
 mm/swap.c            | 9 +--------
 3 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 84255b3da7c1..cfc200673e13 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -331,7 +331,6 @@ extern void mark_page_accessed(struct page *);
 extern void lru_add_drain(void);
 extern void lru_add_drain_cpu(int cpu);
 extern void lru_add_drain_all(void);
-extern void lru_add_drain_all_cpuslocked(void);
 extern void rotate_reclaimable_page(struct page *page);
 extern void deactivate_file_page(struct page *page);
 extern void mark_page_lazyfree(struct page *page);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 832a042134f8..c9f6b418be79 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1641,7 +1641,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
 		goto failed_removal;
-	lru_add_drain_all_cpuslocked();
+	lru_add_drain_all();
 	pfn = scan_movable_pages(start_pfn, end_pfn);
diff --git a/mm/swap.c b/mm/swap.c
index 381e0fe9efbf..8bfdcab9f83e 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -688,7 +688,7 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
 static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
-void lru_add_drain_all_cpuslocked(void)
+void lru_add_drain_all(void)
 	static DEFINE_MUTEX(lock);
 	static struct cpumask has_work;
@@ -724,13 +724,6 @@ void lru_add_drain_all_cpuslocked(void)
-void lru_add_drain_all(void)
-	get_online_cpus();
-	lru_add_drain_all_cpuslocked();
-	put_online_cpus();
  * release_pages - batched put_page()
  * @pages: array of pages to release

Michal Hocko

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