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SubjectRe: [PATCH 1/2] free_pcppages_bulk: do not hold lock when picking pages to free
On Wed, Jan 24, 2018 at 10:30:49AM +0800, Aaron Lu wrote:
> When freeing a batch of pages from Per-CPU-Pages(PCP) back to buddy,
> the zone->lock is held and then pages are chosen from PCP's migratetype
> list. While there is actually no need to do this 'choose part' under
> lock since it's PCP pages, the only CPU that can touch them is us and
> irq is also disabled.
>
> Moving this part outside could reduce lock held time and improve
> performance. Test with will-it-scale/page_fault1 full load:
>
> kernel Broadwell(2S) Skylake(2S) Broadwell(4S) Skylake(4S)
> v4.15-rc4 9037332 8000124 13642741 15728686
> this patch 9608786 +6.3% 8368915 +4.6% 14042169 +2.9% 17433559 +10.8%
>
> What the test does is: starts $nr_cpu processes and each will repeated
> do the following for 5 minutes:
> 1 mmap 128M anonymouse space;
> 2 write access to that space;
> 3 munmap.
> The score is the aggregated iteration.
>
> https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault1.c
>
> Signed-off-by: Aaron Lu <aaron.lu@intel.com>
> ---
> mm/page_alloc.c | 33 +++++++++++++++++++--------------
> 1 file changed, 19 insertions(+), 14 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4093728f292e..a076f754dac1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1113,12 +1113,12 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> int migratetype = 0;
> int batch_free = 0;
> bool isolated_pageblocks;
> + struct list_head head;
> + struct page *page, *tmp;
>
> - spin_lock(&zone->lock);
> - isolated_pageblocks = has_isolate_pageblock(zone);
> + INIT_LIST_HEAD(&head);
>

Declare head as LIST_HEAD(head) and avoid INIT_LIST_HEAD. Otherwise I
think this is safe

Acked-by: Mel Gorman <mgorman@techsingularity.net>

--
Mel Gorman
SUSE Labs

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