Hi all, I tested memcpy with perf bench, and found that in prefault case, When Transparent Hugepage is on, memcpy has worse performance. When THP on is 3.672879 GB/Sec (with prefault), while THP off is 6.190187 GB/Sec (with prefault). I think THP will improve performance, but the test result obviously not the case. Andrea mentioned THP cause "clear_page/copy_page less cache friendly" in http://events.linuxfoundation.org/slides/2011/lfcs/lfcs2011_hpc_arcangeli.pdf. I am not quite understand this, could you please give me some comments, Thanks! I test in Linux-3.4-stable, and my machine info is: Intel(R) Xeon(R) CPU E5520 @ 2.27GHz available: 2 nodes (0-1) node 0 cpus: 0 1 2 3 8 9 10 11 node 0 size: 24567 MB node 0 free: 23550 MB node 1 cpus: 4 5 6 7 12 13 14 15 node 1 size: 24576 MB node 1 free: 23767 MB node distances: node 0 1 0: 10 20 1: 20 10 Below is test result: ---with THP--- #cat /sys/kernel/mm/transparent_hugepage/enabled [always] madvise never #./perf bench mem memcpy -l 1gb -o # Running mem/memcpy benchmark... # Copying 1gb Bytes ... 3.672879 GB/Sec (with prefault) #./perf stat ... Performance counter stats for './perf bench mem memcpy -l 1gb -o': 35455940 cache-misses # 53.504 % of all cache refs [49.45%] 66267785 cache-references [49.78%] 2409 page-faults 450768651 dTLB-loads [50.78%] 24580 dTLB-misses # 0.01% of all dTLB cache hits [51.01%] 1338974202 dTLB-stores [50.63%] 77943 dTLB-misses [50.24%] 697404997 iTLB-loads [49.77%] 274 iTLB-misses # 0.00% of all iTLB cache hits [49.30%] 0.855041819 seconds time elapsed ---no THP--- #cat /sys/kernel/mm/transparent_hugepage/enabled always madvise [never] #./perf bench mem memcpy -l 1gb -o # Running mem/memcpy benchmark... # Copying 1gb Bytes ... 6.190187 GB/Sec (with prefault) #./perf stat ... Performance counter stats for './perf bench mem memcpy -l 1gb -o': 16920763 cache-misses # 98.377 % of all cache refs [50.01%] 17200000 cache-references [50.04%] 524652 page-faults 734365659 dTLB-loads [50.04%] 4986387 dTLB-misses # 0.68% of all dTLB cache hits [50.04%] 1013408298 dTLB-stores [50.04%] 8180817 dTLB-misses [49.97%] 1526642351 iTLB-loads [50.41%] 56 iTLB-misses # 0.00% of all iTLB cache hits [50.21%] 1.025425847 seconds time elapsed Thanks, Jianguo Wu. -- 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>