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mm, page_alloc: drain per-cpu pages from workqueue context 

The per-cpu page allocator can be drained immediately via
drain_all_pages() which sends IPIs to every CPU.  In the next patch, the
per-cpu allocator will only be used for interrupt-safe allocations which
prevents draining it from IPI context.  This patch uses workqueues to
drain the per-cpu lists instead.

This is slower but no slowdown during intensive reclaim was measured and
the paths that use drain_all_pages() are not that sensitive to
performance.  This is particularly true as the path would only be
triggered when reclaim is failing.  It also makes a some sense to avoid
storming a machine with IPIs when it's under memory pressure.  Arguably,
it should be further adjusted so that only one caller at a time is
draining pages but it's beyond the scope of the current patch.

Link: http://lkml.kernel.org/r/20170123153906.3122-4-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman 2017-02-24 14:56:32 -08:00 committed by Linus Torvalds
parent 9cd7555875
commit 0ccce3b924
1 changed files with 37 additions and 7 deletions
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44
mm/page_alloc.c
View File

@ -2339,19 +2339,21 @@ void drain_local_pages(struct zone *zone)
drain_pages(cpu);
}
static void drain_local_pages_wq(struct work_struct *work)
{
drain_local_pages(NULL);
}
/*
* Spill all the per-cpu pages from all CPUs back into the buddy allocator.
*
* When zone parameter is non-NULL, spill just the single zone's pages.
*
* Note that this code is protected against sending an IPI to an offline
* CPU but does not guarantee sending an IPI to newly hotplugged CPUs:
* on_each_cpu_mask() blocks hotplug and won't talk to offlined CPUs but
* nothing keeps CPUs from showing up after we populated the cpumask and
* before the call to on_each_cpu_mask().
* Note that this can be extremely slow as the draining happens in a workqueue.
*/
void drain_all_pages(struct zone *zone)
{
struct work_struct __percpu *works;
int cpu;
/*
@ -2360,6 +2362,17 @@ void drain_all_pages(struct zone *zone)
*/
static cpumask_t cpus_with_pcps;
/* Workqueues cannot recurse */
if (current->flags & PF_WQ_WORKER)
return;
/*
* As this can be called from reclaim context, do not reenter reclaim.
* An allocation failure can be handled, it's simply slower
*/
get_online_cpus();
works = alloc_percpu_gfp(struct work_struct, GFP_ATOMIC);
/*
* We don't care about racing with CPU hotplug event
* as offline notification will cause the notified
@ -2390,8 +2403,25 @@ void drain_all_pages(struct zone *zone)
else
cpumask_clear_cpu(cpu, &cpus_with_pcps);
}
on_each_cpu_mask(&cpus_with_pcps, (smp_call_func_t) drain_local_pages,
zone, 1);
if (works) {
for_each_cpu(cpu, &cpus_with_pcps) {
struct work_struct *work = per_cpu_ptr(works, cpu);
INIT_WORK(work, drain_local_pages_wq);
schedule_work_on(cpu, work);
}
for_each_cpu(cpu, &cpus_with_pcps)
flush_work(per_cpu_ptr(works, cpu));
} else {
for_each_cpu(cpu, &cpus_with_pcps) {
struct work_struct work;
INIT_WORK(&work, drain_local_pages_wq);
schedule_work_on(cpu, &work);
flush_work(&work);
}
}
put_online_cpus();
}
#ifdef CONFIG_HIBERNATION