On Wed, Feb 16, 2011 at 09:00:59AM +0900, Minchan Kim wrote:
> On Wed, Feb 16, 2011 at 7:38 AM, Jack Steiner <steiner@xxxxxxx> wrote:
> >
> > Heavy swapping within a cpuset causes frequent calls to drain_all_pages().
> > This sends IPIs to all cpus to free PCP pages. In most cases, there are
> > no pages to be freed on cpus outside of the swapping cpuset.
> >
> > Add checks to minimize locking and updates to potentially hot cachelines.
> > Before acquiring locks, do a quick check to see if any pages are in the PCP
> > queues. Exit if none.
> >
> > On a 128 node SGI UV system, this reduced the IPI overhead to cpus outside of the
> > swapping cpuset by 38% and improved time to run a pass of the swaping test
> > from 98 sec to 51 sec. These times are obviously test & configuration
> > dependent but the improvements are significant.
> >
> >
> > Signed-off-by: Jack Steiner <steiner@xxxxxxx>
> >
> > ---
> > mm/page_alloc.c | 14 ++++++++++++++
> > 1 file changed, 14 insertions(+)
> >
> > Index: linux/mm/page_alloc.c
> > ===================================================================
> > --- linux.orig/mm/page_alloc.c 2011-02-15 16:28:36.165921713 -0600
> > +++ linux/mm/page_alloc.c 2011-02-15 16:29:43.085502487 -0600
> > @@ -592,10 +592,24 @@ static void free_pcppages_bulk(struct zo
> > int batch_free = 0;
> > int to_free = count;
> >
> > + /*
> > + * Quick scan of zones. If all are empty, there is nothing to do.
> > + */
> > + for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++) {
> > + struct list_head *list;
> > +
> > + list = &pcp->lists[migratetype];
> > + if (!list_empty(list))
> > + break;
> > + }
> > + if (migratetype == MIGRATE_PCPTYPES)
> > + return;
> > +
> > spin_lock(&zone->lock);
> > zone->all_unreclaimable = 0;
> > zone->pages_scanned = 0;
> >
> > + migratetype = 0;
> > while (to_free) {
> > struct page *page;
> > struct list_head *list;
> >
> > --
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> >
>
> It does make sense to me.
> Although new code looks to be rather costly in small box, anyway we
> use the same logic in while loop so cache would be hot. so cost would
> be little.
>
> But how about this? This one never affect fast-critical path.
Yes. Much cleaner. And even better, as David points out it is already in the tree.
I did my original testing on a 2.6.32 distro kernel & missed the fact that this was
recently fixed upstream.
My patch from yesterday can be discarded.
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ff7e158..2dfb61a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1095,8 +1095,10 @@ static void drain_pages(unsigned int cpu)
> pset = per_cpu_ptr(zone->pageset, cpu);
>
> pcp = &pset->pcp;
> - free_pcppages_bulk(zone, pcp->count, pcp);
> - pcp->count = 0;
> + if (pcp->count > 0) {
> + free_pcppages_bulk(zone, pcp->count, pcp);
> + pcp->count = 0;
> + }
> local_irq_restore(flags);
> }
> }
>
>
>
> --
> Kind regards,
> Minchan Kim
--
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