On Wed, Feb 03, 2016 at 07:42:01AM -0800, Dave Hansen wrote: > On 02/03/2016 07:14 AM, Kirill A. Shutemov wrote: > > But the new variant is somewhat slower. Current helpers iterates over > > VMAs the compound page is mapped to, and then over ptes within this VMA. > > New helpers iterates over small page, then over VMA the small page > > mapped to, and only then find relevant pte. > > The code simplification here is really attractive. Can you quantify > what the slowdown is? Is it noticeable, or would it be in the noise > during all the other stuff that happens under memory pressure? Okay, here's more realistic scenario: migration 8GiB worth of THP. Testcase: #define _GNU_SOURCE #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/mman.h> #include <linux/mempolicy.h> #include <numaif.h> #define MB (1024UL * 1024) #define SIZE (4 * 1024 * 2 * MB) #define BASE ((void *)0x400000000000) #include <time.h> void timespec_diff(struct timespec *start, struct timespec *stop, struct timespec *result) { if ((stop->tv_nsec - start->tv_nsec) < 0) { result->tv_sec = stop->tv_sec - start->tv_sec - 1; result->tv_nsec = stop->tv_nsec - start->tv_nsec + 1000000000; } else { result->tv_sec = stop->tv_sec - start->tv_sec; result->tv_nsec = stop->tv_nsec - start->tv_nsec; } } int main() { char *p; unsigned long ret, node_mask; struct timespec start, stop, result; node_mask = 0b01; ret = set_mempolicy(MPOL_BIND, &node_mask, 64); if (ret == -1) perror("set_mempolicy"), exit(1); p = mmap(BASE, SIZE, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0); if (p == MAP_FAILED) perror("mmap"), exit(1); system("grep thp /proc/vmstat"); clock_gettime(CLOCK_MONOTONIC, &start); node_mask = 0b10; ret = mbind(p, SIZE, MPOL_BIND, &node_mask, 64, MPOL_MF_MOVE); if (ret == -1) perror("mbind"), exit(1); clock_gettime(CLOCK_MONOTONIC, &stop); system("grep thp /proc/vmstat"); timespec_diff(&start, &stop, &result); printf("--------------------------\n"); printf("%ld.%09lds\n", result.tv_sec, result.tv_nsec); return 0; } Baseline: 25.146 ± 0.141 Patched: 28.684 ± 0.298 Slowdown: 1.14x Can we tolerate this? -- Kirill A. Shutemov -- 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>