Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context | From | Andrey Ryabinin <> | Date | Wed, 5 Apr 2017 13:31:23 +0300 |
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On 04/04/2017 12:41 PM, Michal Hocko wrote: > On Thu 30-03-17 17:48:39, Andrey Ryabinin wrote: >> From: Andrey Ryabinin <aryabinin@virtuozzo.com> >> Subject: mm/vmalloc: allow to call vfree() in atomic context fix >> >> Don't spawn worker if we already purging. >> >> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > > I would rather put this into a separate patch. Ideally with some numners > as this is an optimization... >
It's quite simple optimization and don't think that this deserves to be a separate patch.
But I did some measurements though. With enabled VMAP_STACK=y and NR_CACHED_STACK changed to 0 running fork() 100000 times gives this:
With optimization:
~ # grep try_purge /proc/kallsyms ffffffff811d0dd0 t try_purge_vmap_area_lazy ~ # perf stat --repeat 10 -ae workqueue:workqueue_queue_work --filter 'function == 0xffffffff811d0dd0' ./fork
Performance counter stats for 'system wide' (10 runs):
15 workqueue:workqueue_queue_work ( +- 0.88% )
1.615368474 seconds time elapsed ( +- 0.41% )
Without optimization: ~ # grep try_purge /proc/kallsyms ffffffff811d0dd0 t try_purge_vmap_area_lazy ~ # perf stat --repeat 10 -ae workqueue:workqueue_queue_work --filter 'function == 0xffffffff811d0dd0' ./fork
Performance counter stats for 'system wide' (10 runs):
30 workqueue:workqueue_queue_work ( +- 1.31% )
1.613231060 seconds time elapsed ( +- 0.38% )
So there is no measurable difference on the test itself, but we queue twice more jobs without this optimization. It should decrease load of kworkers.
>> --- >> mm/vmalloc.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >> index ea1b4ab..88168b8 100644 >> --- a/mm/vmalloc.c >> +++ b/mm/vmalloc.c >> @@ -737,7 +737,8 @@ static void free_vmap_area_noflush(struct vmap_area *va) >> /* After this point, we may free va at any time */ >> llist_add(&va->purge_list, &vmap_purge_list); >> >> - if (unlikely(nr_lazy > lazy_max_pages())) >> + if (unlikely(nr_lazy > lazy_max_pages()) && >> + !mutex_is_locked(&vmap_purge_lock)) >> schedule_work(&purge_vmap_work); >> } >> >> -- >> 2.10.2 >> >
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