Re: [PATCH v2] mm: huge_memory: a new debugfs interface for splitting THP tests.
From: Yang Shi
Date: Wed Mar 10 2021 - 20:13:35 EST
On Wed, Mar 10, 2021 at 7:36 AM Zi Yan <zi.yan@xxxxxxxx> wrote:
>
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> We do not have a direct user interface of splitting the compound page
> backing a THP and there is no need unless we want to expose the THP
> implementation details to users. Adding an interface for debugging.
>
> By writing "<pid>,<vaddr_start>,<vaddr_end>" to
> <debugfs>/split_huge_pages_in_range_pid, THPs within the given virtual
Can we reuse the existing split_huge_page knob instead of creating a new one?
Two knobs for splitting huge pages on debugging purpose seem
overkilling to me IMHO. I'm wondering if we could check if a special
value (e.g. 1 or -1) is written then split all THPs as split_huge_page
knob does?
I don't think this interface is used widely so the risk should be very
low for breaking userspace.
> address range from the process with the given pid are split. It is used
> to test split_huge_page function. In addition, a selftest program is
> added to tools/testing/selftests/vm to utilize the interface by
> splitting PMD THPs and PTE-mapped THPs.
>
> Changelog:
>
> From v1:
>
> 1. Removed unnecessary calling to vma_migratable, spotted by kernel test
> robot <lkp@xxxxxxxxx>.
> 2. Dropped the use of find_mm_struct and code it directly, since there
> is no need for the permission check in that function and the function
> is only available when migration is on.
> 3. Added some comments in the selftest program to clarify how PTE-mapped
> THPs are formed.
>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
> mm/huge_memory.c | 112 ++++++
> tools/testing/selftests/vm/.gitignore | 1 +
> tools/testing/selftests/vm/Makefile | 1 +
> .../selftests/vm/split_huge_page_test.c | 320 ++++++++++++++++++
> 4 files changed, 434 insertions(+)
> create mode 100644 tools/testing/selftests/vm/split_huge_page_test.c
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index bff92dea5ab3..7797e8b2aba0 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -7,6 +7,7 @@
>
> #include <linux/mm.h>
> #include <linux/sched.h>
> +#include <linux/sched/mm.h>
> #include <linux/sched/coredump.h>
> #include <linux/sched/numa_balancing.h>
> #include <linux/highmem.h>
> @@ -2965,10 +2966,121 @@ static int split_huge_pages_set(void *data, u64 val)
> DEFINE_DEBUGFS_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
> "%llu\n");
>
> +static ssize_t split_huge_pages_in_range_pid_write(struct file *file,
> + const char __user *buf, size_t count, loff_t *ppops)
> +{
> + static DEFINE_MUTEX(mutex);
> + ssize_t ret;
> + char input_buf[80]; /* hold pid, start_vaddr, end_vaddr */
> + int pid;
> + unsigned long vaddr_start, vaddr_end, addr;
> + struct task_struct *task;
> + struct mm_struct *mm;
> + unsigned long total = 0, split = 0;
> +
> + ret = mutex_lock_interruptible(&mutex);
> + if (ret)
> + return ret;
> +
> + ret = -EFAULT;
> +
> + memset(input_buf, 0, 80);
> + if (copy_from_user(input_buf, buf, min_t(size_t, count, 80)))
> + goto out;
> +
> + input_buf[79] = '\0';
> + ret = sscanf(input_buf, "%d,0x%lx,0x%lx", &pid, &vaddr_start, &vaddr_end);
> + if (ret != 3) {
> + ret = -EINVAL;
> + goto out;
> + }
> + vaddr_start &= PAGE_MASK;
> + vaddr_end &= PAGE_MASK;
> +
> + ret = strlen(input_buf);
> + pr_debug("split huge pages in pid: %d, vaddr: [%lx - %lx]\n",
> + pid, vaddr_start, vaddr_end);
> +
> + /* Find the task_struct from pid */
> + rcu_read_lock();
> + task = find_task_by_vpid(pid);
> + if (!task) {
> + rcu_read_unlock();
> + ret = -ESRCH;
> + goto out;
> + }
> + get_task_struct(task);
> + rcu_read_unlock();
> +
> + /* Find the mm_struct */
> + mm = get_task_mm(task);
> + put_task_struct(task);
> +
> + if (!mm) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + mmap_read_lock(mm);
> + /*
> + * always increase addr by PAGE_SIZE, since we could have a PTE page
> + * table filled with PTE-mapped THPs, each of which is distinct.
> + */
> + for (addr = vaddr_start; addr < vaddr_end; addr += PAGE_SIZE) {
> + struct vm_area_struct *vma = find_vma(mm, addr);
> + unsigned int follflags;
> + struct page *page;
> +
> + if (!vma || addr < vma->vm_start)
> + break;
> +
> + /* FOLL_DUMP to ignore special (like zero) pages */
> + follflags = FOLL_GET | FOLL_DUMP;
> + page = follow_page(vma, addr, follflags);
> +
> + if (IS_ERR(page))
> + break;
> + if (!page)
> + break;
> +
> + if (!is_transparent_hugepage(page))
> + continue;
> +
> + total++;
> + if (!can_split_huge_page(compound_head(page), NULL))
> + continue;
> +
> + if (!trylock_page(page))
> + continue;
> +
> + if (!split_huge_page(page))
> + split++;
> +
> + unlock_page(page);
> + put_page(page);
> + }
> + mmap_read_unlock(mm);
> + mmput(mm);
> +
> + pr_debug("%lu of %lu THP split\n", split, total);
> +out:
> + mutex_unlock(&mutex);
> + return ret;
> +
> +}
> +
> +static const struct file_operations split_huge_pages_in_range_pid_fops = {
> + .owner = THIS_MODULE,
> + .write = split_huge_pages_in_range_pid_write,
> + .llseek = no_llseek,
> +};
> +
> static int __init split_huge_pages_debugfs(void)
> {
> debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
> &split_huge_pages_fops);
> + debugfs_create_file("split_huge_pages_in_range_pid", 0200, NULL, NULL,
> + &split_huge_pages_in_range_pid_fops);
> return 0;
> }
> late_initcall(split_huge_pages_debugfs);
> diff --git a/tools/testing/selftests/vm/.gitignore b/tools/testing/selftests/vm/.gitignore
> index 9a35c3f6a557..1f651e85ed60 100644
> --- a/tools/testing/selftests/vm/.gitignore
> +++ b/tools/testing/selftests/vm/.gitignore
> @@ -22,3 +22,4 @@ map_fixed_noreplace
> write_to_hugetlbfs
> hmm-tests
> local_config.*
> +split_huge_page_test
> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> index d42115e4284d..4cbc91d6869f 100644
> --- a/tools/testing/selftests/vm/Makefile
> +++ b/tools/testing/selftests/vm/Makefile
> @@ -42,6 +42,7 @@ TEST_GEN_FILES += on-fault-limit
> TEST_GEN_FILES += thuge-gen
> TEST_GEN_FILES += transhuge-stress
> TEST_GEN_FILES += userfaultfd
> +TEST_GEN_FILES += split_huge_page_test
>
> ifeq ($(MACHINE),x86_64)
> CAN_BUILD_I386 := $(shell ./../x86/check_cc.sh $(CC) ../x86/trivial_32bit_program.c -m32)
> diff --git a/tools/testing/selftests/vm/split_huge_page_test.c b/tools/testing/selftests/vm/split_huge_page_test.c
> new file mode 100644
> index 000000000000..0c6532dfdd96
> --- /dev/null
> +++ b/tools/testing/selftests/vm/split_huge_page_test.c
> @@ -0,0 +1,320 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * A test of splitting PMD THPs and PTE-mapped THPs from a specified virtual
> + * address range in a process via <debugfs>/split_huge_pages_in_range_pid
> + * interface.
> + */
> +
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include "numa.h"
> +#include <unistd.h>
> +#include <errno.h>
> +#include <inttypes.h>
> +#include <string.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <fcntl.h>
> +#include <sys/mman.h>
> +#include <sys/time.h>
> +#include <sys/wait.h>
> +#include <malloc.h>
> +#include <stdbool.h>
> +
> +uint64_t pagesize;
> +unsigned int pageshift;
> +uint64_t pmd_pagesize;
> +
> +#define PMD_SIZE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
> +#define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages_in_range_pid"
> +#define SMAP_PATH "/proc/self/smaps"
> +#define INPUT_MAX 80
> +
> +#define PFN_MASK ((1UL<<55)-1)
> +#define KPF_THP (1UL<<22)
> +
> +int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
> +{
> + uint64_t paddr;
> + uint64_t page_flags;
> +
> + if (pagemap_file) {
> + pread(pagemap_file, &paddr, sizeof(paddr),
> + ((long)vaddr >> pageshift) * sizeof(paddr));
> +
> + if (kpageflags_file) {
> + pread(kpageflags_file, &page_flags, sizeof(page_flags),
> + (paddr & PFN_MASK) * sizeof(page_flags));
> +
> + return !!(page_flags & KPF_THP);
> + }
> + }
> + return 0;
> +}
> +
> +
> +static uint64_t read_pmd_pagesize(void)
> +{
> + int fd;
> + char buf[20];
> + ssize_t num_read;
> +
> + fd = open(PMD_SIZE_PATH, O_RDONLY);
> + if (fd == -1) {
> + perror("Open hpage_pmd_size failed");
> + exit(EXIT_FAILURE);
> + }
> + num_read = read(fd, buf, 19);
> + if (num_read < 1) {
> + close(fd);
> + perror("Read hpage_pmd_size failed");
> + exit(EXIT_FAILURE);
> + }
> + buf[num_read] = '\0';
> + close(fd);
> +
> + return strtoul(buf, NULL, 10);
> +}
> +
> +static int write_file(const char *path, const char *buf, size_t buflen)
> +{
> + int fd;
> + ssize_t numwritten;
> +
> + fd = open(path, O_WRONLY);
> + if (fd == -1)
> + return 0;
> +
> + numwritten = write(fd, buf, buflen - 1);
> + close(fd);
> + if (numwritten < 1)
> + return 0;
> +
> + return (unsigned int) numwritten;
> +}
> +
> +static void write_debugfs(int pid, uint64_t vaddr_start, uint64_t vaddr_end)
> +{
> + char input[INPUT_MAX];
> + int ret;
> +
> + ret = snprintf(input, INPUT_MAX, "%d,0x%lx,0x%lx", pid, vaddr_start,
> + vaddr_end);
> + if (ret >= INPUT_MAX) {
> + printf("%s: Debugfs input is too long\n", __func__);
> + exit(EXIT_FAILURE);
> + }
> +
> + if (!write_file(SPLIT_DEBUGFS, input, ret + 1)) {
> + perror(SPLIT_DEBUGFS);
> + exit(EXIT_FAILURE);
> + }
> +}
> +
> +#define MAX_LINE_LENGTH 500
> +
> +static bool check_for_pattern(FILE *fp, const char *pattern, char *buf)
> +{
> + while (fgets(buf, MAX_LINE_LENGTH, fp) != NULL) {
> + if (!strncmp(buf, pattern, strlen(pattern)))
> + return true;
> + }
> + return false;
> +}
> +
> +static uint64_t check_huge(void *addr)
> +{
> + uint64_t thp = 0;
> + int ret;
> + FILE *fp;
> + char buffer[MAX_LINE_LENGTH];
> + char addr_pattern[MAX_LINE_LENGTH];
> +
> + ret = snprintf(addr_pattern, MAX_LINE_LENGTH, "%08lx-",
> + (unsigned long) addr);
> + if (ret >= MAX_LINE_LENGTH) {
> + printf("%s: Pattern is too long\n", __func__);
> + exit(EXIT_FAILURE);
> + }
> +
> +
> + fp = fopen(SMAP_PATH, "r");
> + if (!fp) {
> + printf("%s: Failed to open file %s\n", __func__, SMAP_PATH);
> + exit(EXIT_FAILURE);
> + }
> + if (!check_for_pattern(fp, addr_pattern, buffer))
> + goto err_out;
> +
> + /*
> + * Fetch the AnonHugePages: in the same block and check the number of
> + * hugepages.
> + */
> + if (!check_for_pattern(fp, "AnonHugePages:", buffer))
> + goto err_out;
> +
> + if (sscanf(buffer, "AnonHugePages:%10ld kB", &thp) != 1) {
> + printf("Reading smap error\n");
> + exit(EXIT_FAILURE);
> + }
> +
> +err_out:
> + fclose(fp);
> + return thp;
> +}
> +
> +void split_pmd_thp(void)
> +{
> + char *one_page;
> + size_t len = 4 * pmd_pagesize;
> + uint64_t thp_size;
> + size_t i;
> +
> + one_page = memalign(pmd_pagesize, len);
> +
> + madvise(one_page, len, MADV_HUGEPAGE);
> +
> + for (i = 0; i < len; i++)
> + one_page[i] = (char)i;
> +
> + thp_size = check_huge(one_page);
> + if (!thp_size) {
> + printf("No THP is allocatd");
> + exit(EXIT_FAILURE);
> + }
> +
> + /* split all THPs */
> + write_debugfs(getpid(), (uint64_t)one_page, (uint64_t)one_page + len);
> +
> + for (i = 0; i < len; i++)
> + if (one_page[i] != (char)i) {
> + printf("%ld byte corrupted\n", i);
> + exit(EXIT_FAILURE);
> + }
> +
> +
> + thp_size = check_huge(one_page);
> + if (thp_size) {
> + printf("Still %ld kB AnonHugePages not split\n", thp_size);
> + exit(EXIT_FAILURE);
> + }
> +
> + printf("Split huge pages successful\n");
> + free(one_page);
> +}
> +
> +void split_pte_mapped_thp(void)
> +{
> + char *one_page, *pte_mapped, *pte_mapped2;
> + size_t len = 4 * pmd_pagesize;
> + uint64_t thp_size;
> + size_t i;
> + const char *pagemap_template = "/proc/%d/pagemap";
> + const char *kpageflags_proc = "/proc/kpageflags";
> + char pagemap_proc[255];
> + int pagemap_fd;
> + int kpageflags_fd;
> +
> + if (snprintf(pagemap_proc, 255, pagemap_template, getpid()) < 0) {
> + perror("get pagemap proc error");
> + exit(EXIT_FAILURE);
> + }
> + pagemap_fd = open(pagemap_proc, O_RDONLY);
> +
> + if (pagemap_fd == -1) {
> + perror("read pagemap:");
> + exit(EXIT_FAILURE);
> + }
> +
> + kpageflags_fd = open(kpageflags_proc, O_RDONLY);
> +
> + if (kpageflags_fd == -1) {
> + perror("read kpageflags:");
> + exit(EXIT_FAILURE);
> + }
> +
> + one_page = mmap((void *)(1UL << 30), len, PROT_READ | PROT_WRITE,
> + MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +
> + madvise(one_page, len, MADV_HUGEPAGE);
> +
> + for (i = 0; i < len; i++)
> + one_page[i] = (char)i;
> +
> + thp_size = check_huge(one_page);
> + if (!thp_size) {
> + printf("No THP is allocatd");
> + exit(EXIT_FAILURE);
> + }
> +
> + /* remap the first pagesize of first THP */
> + pte_mapped = mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE);
> +
> + /* remap the Nth pagesize of Nth THP */
> + for (i = 1; i < 4; i++) {
> + pte_mapped2 = mremap(one_page + pmd_pagesize * i + pagesize * i,
> + pagesize, pagesize,
> + MREMAP_MAYMOVE|MREMAP_FIXED,
> + pte_mapped + pagesize * i);
> + if (pte_mapped2 == (char *)-1) {
> + perror("mremap failed");
> + exit(EXIT_FAILURE);
> + }
> + }
> +
> + /* smap does not show THPs after mremap, use kpageflags instead */
> + thp_size = 0;
> + for (i = 0; i < pagesize * 4; i++)
> + if (i % pagesize == 0 &&
> + is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
> + thp_size++;
> +
> + if (thp_size != 4) {
> + printf("Some THPs are missing during mremap\n");
> + exit(EXIT_FAILURE);
> + }
> +
> + /* split all remapped THPs */
> + write_debugfs(getpid(), (uint64_t)pte_mapped,
> + (uint64_t)pte_mapped + pagesize * 4);
> +
> + /* smap does not show THPs after mremap, use kpageflags instead */
> + thp_size = 0;
> + for (i = 0; i < pagesize * 4; i++) {
> + if (pte_mapped[i] != (char)i) {
> + printf("%ld byte corrupted\n", i);
> + exit(EXIT_FAILURE);
> + }
> + if (i % pagesize == 0 &&
> + is_backed_by_thp(&pte_mapped[i], pagemap_fd, kpageflags_fd))
> + thp_size++;
> + }
> +
> + if (thp_size) {
> + printf("Still %ld THPs not split\n", thp_size);
> + exit(EXIT_FAILURE);
> + }
> +
> + printf("Split PTE-mapped huge pages successful\n");
> + munmap(one_page, len);
> + close(pagemap_fd);
> + close(kpageflags_fd);
> +}
> +
> +int main(int argc, char **argv)
> +{
> + if (geteuid() != 0) {
> + printf("Please run the benchmark as root\n");
> + exit(EXIT_FAILURE);
> + }
> +
> + pagesize = getpagesize();
> + pageshift = ffs(pagesize) - 1;
> + pmd_pagesize = read_pmd_pagesize();
> +
> + split_pmd_thp();
> + split_pte_mapped_thp();
> +
> + return 0;
> +}
> --
> 2.30.1
>