The patch titled
Subject: mm: drop hotplug lock from lru_add_drain_all()
has been added to the -mm tree. Its filename is
mm-drop-hotplug-lock-from-lru_add_drain_all.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-drop-hotplug-lock-from-lru_add_drain_all.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-drop-hotplug-lock-from-lru_add_drain_all.patch
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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
Subject: 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 avoid the locking as lru_add_drain_all() is used in many places.
It seems that this is not all that hard to achieve actually.
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 completely.
[1] http://lkml.kernel.org/r/089e0825eec8955c1f055c83d476@xxxxxxxxxx
[add a cpu hotplug locking interaction as per tglx]
Link: http://lkml.kernel.org/r/20171116120535.23765-1-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/swap.h | 1 -
mm/memory_hotplug.c | 2 +-
mm/swap.c | 16 ++++++++--------
3 files changed, 9 insertions(+), 10 deletions(-)
diff -puN include/linux/swap.h~mm-drop-hotplug-lock-from-lru_add_drain_all include/linux/swap.h
--- a/include/linux/swap.h~mm-drop-hotplug-lock-from-lru_add_drain_all
+++ a/include/linux/swap.h
@@ -332,7 +332,6 @@ extern void mark_page_accessed(struct pa
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 -puN mm/memory_hotplug.c~mm-drop-hotplug-lock-from-lru_add_drain_all mm/memory_hotplug.c
--- a/mm/memory_hotplug.c~mm-drop-hotplug-lock-from-lru_add_drain_all
+++ a/mm/memory_hotplug.c
@@ -1641,7 +1641,7 @@ repeat:
goto failed_removal;
cond_resched();
- lru_add_drain_all_cpuslocked();
+ lru_add_drain_all();
drain_all_pages(zone);
pfn = scan_movable_pages(start_pfn, end_pfn);
diff -puN mm/swap.c~mm-drop-hotplug-lock-from-lru_add_drain_all mm/swap.c
--- a/mm/swap.c~mm-drop-hotplug-lock-from-lru_add_drain_all
+++ a/mm/swap.c
@@ -688,7 +688,14 @@ static void lru_add_drain_per_cpu(struct
static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
-void lru_add_drain_all_cpuslocked(void)
+/*
+ * Doesn't need any cpu hotplug locking because we do rely on per-cpu
+ * kworkers being shut down before our page_alloc_cpu_dead callback is
+ * executed on the offlined cpu.
+ * Calling this function with cpu hotplug locks held can actually lead
+ * to obscure indirect dependencies via WQ context.
+ */
+void lru_add_drain_all(void)
{
static DEFINE_MUTEX(lock);
static struct cpumask has_work;
@@ -724,13 +731,6 @@ void lru_add_drain_all_cpuslocked(void)
mutex_unlock(&lock);
}
-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
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-memory_hotplug-do-not-back-off-draining-pcp-free-pages-from-kworker-context.patch
mm-drop-hotplug-lock-from-lru_add_drain_all.patch
mm-hugetlb-drop-hugepages_treat_as_movable-sysctl.patch
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