Messages in this thread | | | Date | Wed, 6 Nov 2013 15:41:20 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] mm: cma: free cma page to buddy instead of being cpu hot page |
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On Wed, 6 Nov 2013 15:43:02 +0900 Minchan Kim <minchan@kernel.org> wrote:
> > The added overhead is pretty small - just a comparison of a local with > > a constant. And that cost is not incurred for MIGRATE_UNMOVABLE, > > MIGRATE_RECLAIMABLE and MIGRATE_MOVABLE, which are the common cases > > (yes?). > > True but bloat code might affect icache so we should be careful. > And what Mel has a concern is about zone->lock, which would be more contended. > I agree his opinion. > > In addition, I think the gain is marginal because normally CMA is big range > so free_contig_range in dma release path will fill per_cpu_pages with freed pages > easily so it could drain per_cpu_pages frequently so race which steal page from > per_cpu_pages is not big, I guess. > > Morever, we could change free_contig_range with batch_free_page which would > be useful for other cases if they want to free many number of pages > all at once. > > The bottom line is we need *number and real scenario* for that.
Well yes, quantitative results are always good to have with a patch like this.
It doesn't actually compile (missing a "}"), which doesn't inspire confidence. I'll make the patch go away for now
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