On Thu, Dec 06, 2012 at 11:38:47AM -0800, Linus Torvalds wrote: > Ok, I've applied the patch. > Thanks. > Mel, some grepping shows that there is an old line that does > > end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages); > > which looks bogus. It's bogus. The impact is that multiple compaction attempts may be needed to clear a particular block for allocation. THP allocation success rate under stress will be lower and the latency before a range of pages is collapsed by khugepaged to a huge page will be higher. The impact of this is less and it should not result in a bug like Henrik's An attentive reviewer is going to exclaim that GFP_ATOMIC allocations for jumbo frames is impacted by this but it isn't. Even with this bogus walk, compaction will be clearing SWAP_CLUSTER_MAX contiguous chunks which is enough for jumbo frames. > That should probably also use "+ 1" instead. But > I'll consider that an independent issue, so I applied the one patch > regardless. > > There is also a > > low_pfn += pageblock_nr_pages; > low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1; > > that looks suspicious for similar reasons. Maybe > > low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1; > This one is working by co-incidence because the low_pfn will be aligned in most cases. If it was outright broken then CMA would never work either. > instead? Although that *can* result in the same low_pfn in the end, so > maybe that one was correct after all? I just did some grepping, no > actual semantic analysis... > They need fixing but the impact is much less severe and does not justify delaying 3.8 over unlike the other last-minute fixes. My performance writing patches during talks was less than stellar yesterday so I'll avoid a repeat performance and follow up with Andrew early next week with a cc to -stable. It'll also give me a chance to run the patches through the highalloc stress tests and confirm that allocation success rate is higher and latency lower as would be expected by such a fix. Thanks. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>