On Wed, Nov 23, 2016 at 04:37:06PM +0100, Vlastimil Babka wrote:
> On 11/21/2016 04:55 PM, Mel Gorman wrote:
>
> ...
>
> > hackbench was also tested with both socket and pipes and both processes
> > and threads and the results are interesting in terms of how variability
> > is imapcted
> >
> > 1-socket machine -- pipes and processes
> > 4.9.0-rc5 4.9.0-rc5
> > vanilla highmark-v1r12
> > Amean 1 12.9637 ( 0.00%) 12.9570 ( 0.05%)
> > Amean 3 13.4770 ( 0.00%) 13.4447 ( 0.24%)
> > Amean 5 18.5333 ( 0.00%) 19.0917 ( -3.01%)
> > Amean 7 24.5690 ( 0.00%) 26.1010 ( -6.24%)
> > Amean 12 39.7990 ( 0.00%) 40.6763 ( -2.20%)
> > Amean 16 56.0520 ( 0.00%) 58.2530 ( -3.93%)
>
> Here, higher values are better or worse?
>
Higher values are worse.
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index 0f088f3a2fed..02eb24d90d70 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -255,6 +255,24 @@ enum zone_watermarks {
> > NR_WMARK
> > };
> >
> > +/*
> > + * One per migratetype for order-0 pages and one per high-order up to
> > + * and including PAGE_ALLOC_COSTLY_ORDER. This may allow unmovable
> > + * allocations to contaminate reclaimable pageblocks if high-order
> > + * pages are heavily used.
> > + */
> > +#define NR_PCP_LISTS (MIGRATE_PCPTYPES + PAGE_ALLOC_COSTLY_ORDER + 1)
>
> Should it be "- 1" instead of "+ 1"?
>
Yes.
> > +
> > +static inline unsigned int pindex_to_order(unsigned int pindex)
> > +{
> > + return pindex < MIGRATE_PCPTYPES ? 0 : pindex - MIGRATE_PCPTYPES + 1;
> > +}
> > +
> > +static inline unsigned int order_to_pindex(int migratetype, unsigned int order)
> > +{
> > + return (order == 0) ? migratetype : MIGRATE_PCPTYPES - 1 + order;
>
> Here I think that "MIGRATE_PCPTYPES + order - 1" would be easier to
> understand as the array is for all migratetypes, but the order is shifted?
>
As in migratetypes * costly_order ? That would be excessively large.
> > @@ -1083,10 +1083,12 @@ static bool bulkfree_pcp_prepare(struct page *page)
> > * pinned" detection logic.
> > */
> > static void free_pcppages_bulk(struct zone *zone, int count,
> > - struct per_cpu_pages *pcp)
> > + struct per_cpu_pages *pcp,
> > + int migratetype)
> > {
> > - int migratetype = 0;
> > - int batch_free = 0;
> > + unsigned int pindex = 0;
>
> Should pindex be initialized to migratetype to match the list below?
>
Functionally it doesn't matter. It affects which list is tried first if
the preferred list is empty. Arguably it would make more sense to init
it to NR_PCP_LISTS - 1 so all order-0 lists are always drained before the
high-order pages but there is not much justification for that.
I'll take your suggestion until there is data supporting that high-order
caches should be preserved.
Thanks.
--
Mel Gorman
SUSE Labs
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