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workloads >>> that have shown to benefit from hugepages to do so, without regressin= g >>> workloads that wouldn't benefit. This will allow such types of >>> workloads to be run/stacked on the same machine. >>> >>> It also helps in rolling out hugepages in hyperscaler configurations >>> for workloads that benefit from them, where a single THP policy is >>> likely to be used across the entire fleet, and prctl will help overri= de it. >>> >>> An advantage of doing it via prctl vs creating a cgroup specific >>> option (like /sys/fs/cgroup/test/memory.transparent_hugepage.enabled)= is >>> that this will work even when there are no cgroups present, and my >>> understanding is there is a strong preference of cgroups controls bei= ng >>> hierarchical which usually means them having a numerical value. >> >> Hi Usama, >> >> Do you mind giving an example on how to change THP policy for a set of= >> processes running in a container (under a cgroup)? > > Hi Zi, > > In our case, we create the processes in the cgroup via systemd. The way= we will enable THP=3Dalways > for processes in a cgroup is in the same way we enable KSM for the cgro= up. > The change in systemd would be very similar to the line in [1], where w= e would set prctl PR_SET_THP_ALWAYS > in exec-invoke. > This is at the start of the process, but you would already know at the = start of the process > whether you want THP=3Dalways for it or not. > > [1] https://github.com/systemd/systemd/blob/2e72d3efafa88c1cb4d9b28dd4a= de7c6ab7be29a/src/core/exec-invoke.c#L5045 You also need to add a new systemd.directives, e.g., MemoryTHP, to pass the THP enablement or disablement info from a systemd config file. And if you find those processes do not benefit from using THPs, you can just change the new "MemoryTHP" config and restart the processes.= Am I getting it? Thanks. >> >> Yafang mentioned that the prctl approach would require restarting all = running >> services[1] and other inflexiblities, so he proposed to use BPF to cha= nge THP >> policy[2]. I wonder if Yafang's issues also apply to your case and if = you >> have a solution to them. >> >> Thanks. >> >> [1] https://lore.kernel.org/linux-mm/CALOAHbCXMi2GaZdHJaNLXxGsJf-hkDTr= ztsQiceaBcJ8d8p3cA@mail.gmail.com/ >> [2] https://lore.kernel.org/linux-mm/20250429024139.34365-1-laoar.shao= @gmail.com/ >>> >>> >>> The output and code of test program is below: >>> >>> [root@vm4 vmuser]# echo madvise > /sys/kernel/mm/transparent_hugepage= /enabled >>> [root@vm4 vmuser]# echo inherit > /sys/kernel/mm/transparent_hugepage= /hugepages-2048kB/enabled >>> [root@vm4 vmuser]# ./a.out >>> Default THP setting: >>> THP is not set to 'always'. >>> PR_SET_THP_ALWAYS =3D 1 >>> THP is set to 'always'. >>> PR_SET_THP_ALWAYS =3D 0 >>> THP is not set to 'always'. >>> >>> >>> #include >>> #include >>> #include >>> #include >>> #include >>> #include >>> >>> #define PR_SET_THP_ALWAYS 78 >>> #define SIZE 12 * (2 * 1024 * 1024) // 24 MB >>> >>> void check_smaps(void) { >>> FILE *file =3D fopen("/proc/self/smaps", "r"); >>> if (!file) { >>> perror("fopen"); >>> return; >>> } >>> >>> char line[256]; >>> int is_hugepage =3D 0; >>> while (fgets(line, sizeof(line), file)) { >>> // if (strstr(line, "AnonHugePages:")) >>> // printf("%s\n", line); >>> if (strstr(line, "AnonHugePages:") && strstr(line, "24576 kB"= )) >>> { >>> // printf("%s\n", line); >>> is_hugepage =3D 1; >>> break; >>> } >>> } >>> fclose(file); >>> if (is_hugepage) { >>> printf("THP is set to 'always'.\n"); >>> } else { >>> printf("THP is not set to 'always'.\n"); >>> } >>> } >>> >>> void test_mmap_thp(void) { >>> char *buffer =3D (char *)mmap(NULL, SIZE, PROT_READ | PROT_WRITE,= >>> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); >>> if (buffer =3D=3D MAP_FAILED) { >>> perror("mmap"); >>> return; >>> } >>> // Touch the memory to ensure it's allocated >>> memset(buffer, 0, SIZE); >>> check_smaps(); >>> munmap(buffer, SIZE); >>> } >>> >>> int main() { >>> printf("Default THP setting: \n"); >>> test_mmap_thp(); >>> printf("PR_SET_THP_ALWAYS =3D 1 \n"); >>> prctl(PR_SET_THP_ALWAYS, 1, NULL, NULL, NULL); >>> test_mmap_thp(); >>> printf("PR_SET_THP_ALWAYS =3D 0 \n"); >>> prctl(PR_SET_THP_ALWAYS, 0, NULL, NULL, NULL); >>> test_mmap_thp(); >>> >>> return 0; >>> } >>> >>> >>> Usama Arif (1): >>> prctl: allow overriding system THP policy to always per process >>> >>> include/linux/huge_mm.h | 3 ++- >>> include/linux/mm_types.h | 7 ++----- >>> include/uapi/linux/prctl.h | 3 +++ >>> kernel/sys.c | 16 ++++++++++++++= ++ >>> tools/include/uapi/linux/prctl.h | 3 +++ >>> .../perf/trace/beauty/include/uapi/linux/prctl.h | 3 +++ >>> 6 files changed, 29 insertions(+), 6 deletions(-) >>> >>> -- = >>> 2.47.1 >> >> >> -- >> Best Regards, >> Yan, Zi -- Best Regards, Yan, Zi