Hi, This is the second patchset needed to support THP on ppc64. Some of the changes included in this series are tricky in that it changes the powerpc linux page table walk subtly. We also overload few of the pte flags for ptes at PMD leve (huge page PTEs). This patchset require closer review before merging upstream. I have split the patch series into two patchset, so that we can look at getting prerequisite patches upstream in 3.10. Some numbers: The latency measurements code from Anton found at http://ozlabs.org/~anton/junkcode/latency2001.c 64K page size (With THP support) -------------------------- [root@llmp24l02 test]# ./latency2001 8G 8589934592 428.49 cycles 120.50 ns [root@llmp24l02 test]# ./latency2001 -l 8G 8589934592 471.16 cycles 132.50 ns [root@llmp24l02 test]# echo never > /sys/kernel/mm/transparent_hugepage/enabled [root@llmp24l02 test]# ./latency2001 8G 8589934592 766.52 cycles 215.56 ns [root@llmp24l02 test]# 4K page size (No THP support for 4K) ---------------------------- [root@llmp24l02 test]# ./latency2001 8G 8589934592 814.88 cycles 229.16 ns [root@llmp24l02 test]# ./latency2001 -l 8G 8589934592 463.69 cycles 130.40 ns [root@llmp24l02 test]# We are close to hugetlbfs in latency and we can achieve this with zero config/page reservation. Most of the allocations above are fault allocated. Another test that does 50000000 random access over 1GB area goes from 2.65 seconds to 1.07 seconds with this patchset. split_huge_page impact: --------------------- To look at the performance impact of large page invalidate, I tried the below experiment. The test involved, accessing a large contiguous region of memory location as below for (i = 0; i < size; i += PAGE_SIZE) data[i] = i; We wanted to access the data in sequential order so that we look at the worst case THP performance. Accesing the data in sequential order implies we have the Page table cached and overhead of TLB miss is as minimal as possible. We also don't touch the entire page, because that can result in cache evict. After we touched the full range as above, we now call mprotect on each of that page. A mprotect will result in a hugepage split. This should allow us to measure the impact of hugepage split. for (i = 0; i < size; i += PAGE_SIZE) mprotect(&data[i], PAGE_SIZE, PROT_READ); Split hugepage impact: --------------------- THP enabled: 2.851561705 seconds for test completion THP disable: 3.599146098 seconds for test completion We are 20.7% better than non THP case even when we have all the large pages split. Detailed output: THP enabled: --------------------------------------- [root@llmp24l02 ~]# cat /proc/vmstat | grep thp thp_fault_alloc 0 thp_fault_fallback 0 thp_collapse_alloc 0 thp_collapse_alloc_failed 0 thp_split 0 thp_zero_page_alloc 0 thp_zero_page_alloc_failed 0 [root@llmp24l02 ~]# /root/thp/tools/perf/perf stat -e page-faults,dTLB-load-misses ./split-huge-page-mpro 20G time taken to touch all the data in ns: 2763096913 Performance counter stats for './split-huge-page-mpro 20G': 1,581 page-faults 3,159 dTLB-load-misses 2.851561705 seconds time elapsed [root@llmp24l02 ~]# [root@llmp24l02 ~]# cat /proc/vmstat | grep thp thp_fault_alloc 1279 thp_fault_fallback 0 thp_collapse_alloc 0 thp_collapse_alloc_failed 0 thp_split 1279 thp_zero_page_alloc 0 thp_zero_page_alloc_failed 0 [root@llmp24l02 ~]# 77.05% split-huge-page [kernel.kallsyms] [k] .clear_user_page 7.10% split-huge-page [kernel.kallsyms] [k] .perf_event_mmap_ctx 1.51% split-huge-page split-huge-page-mpro [.] 0x0000000000000a70 0.96% split-huge-page [unknown] [H] 0x000000000157e3bc 0.81% split-huge-page [kernel.kallsyms] [k] .up_write 0.76% split-huge-page [kernel.kallsyms] [k] .perf_event_mmap 0.76% split-huge-page [kernel.kallsyms] [k] .down_write 0.74% split-huge-page [kernel.kallsyms] [k] .lru_add_page_tail 0.61% split-huge-page [kernel.kallsyms] [k] .split_huge_page 0.59% split-huge-page [kernel.kallsyms] [k] .change_protection 0.51% split-huge-page [kernel.kallsyms] [k] .release_pages 0.96% split-huge-page [unknown] [H] 0x000000000157e3bc | |--79.44%-- reloc_start | | | |--86.54%-- .__pSeries_lpar_hugepage_invalidate | | .pSeries_lpar_hugepage_invalidate | | .hpte_need_hugepage_flush | | .split_huge_page | | .__split_huge_page_pmd | | .vma_adjust | | .vma_merge | | .mprotect_fixup | | .SyS_mprotect THP disabled: --------------- [root@llmp24l02 ~]# echo never > /sys/kernel/mm/transparent_hugepage/enabled [root@llmp24l02 ~]# /root/thp/tools/perf/perf stat -e page-faults,dTLB-load-misses ./split-huge-page-mpro 20G time taken to touch all the data in ns: 3513767220 Performance counter stats for './split-huge-page-mpro 20G': 3,27,726 page-faults 3,29,654 dTLB-load-misses 3.599146098 seconds time elapsed [root@llmp24l02 ~]# Changes from V6: * split the patch series into two patchset. * Address review feedback. Changes from V5: * Address review comments * Added new patch to not use hugepd for explcit hugepages. Explicit hugepaes now use PTE format similar to transparent hugepages. * We don't use page->_mapcount for tracking free PTE frags in a PTE page. * rebased to a86d52667d8eda5de39393ce737794403bdce1eb * Tested with libhugetlbfs test suite Changes from V4: * Fix bad page error in page_table_alloc BUG: Bad page state in process stream pfn:f1a59 page:f0000000034dc378 count:1 mapcount:0 mapping: (null) index:0x0 [c000000f322c77d0] [c00000000015e198] .bad_page+0xe8/0x140 [c000000f322c7860] [c00000000015e3c4] .free_pages_prepare+0x1d4/0x1e0 [c000000f322c7910] [c000000000160450] .free_hot_cold_page+0x50/0x230 [c000000f322c79c0] [c00000000003ad18] .page_table_alloc+0x168/0x1c0 Changes from V3: * PowerNV boot fixes Change from V2: * Change patch "powerpc: Reduce PTE table memory wastage" to use much simpler approach for PTE page sharing. * Changes to handle huge pages in KVM code. * Address other review comments Changes from V1 * Address review comments * More patch split * Add batch hpte invalidate for hugepages. Changes from RFC V2: * Address review comments * More code cleanup and patch split Changes from RFC V1: * HugeTLB fs now works * Compile issues fixed * rebased to v3.8 * Patch series reorded so that ppc64 cleanups and MM THP changes are moved early in the series. This should help in picking those patches early. Thanks, -aneesh -- 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>
