Messages in this thread | | | Date | Wed, 23 Nov 2016 16:33:51 +0000 | From | Mel Gorman <> | Subject | Re: [RFC PATCH] mm: page_alloc: High-order per-cpu page allocator |
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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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