Re: [RFC PATCH 1/6] mm: huge_memory: add new debugfs interface to trigger split huge page on any page range.

On Wed, Nov 11, 2020 at 03:40:03PM -0500, Zi Yan wrote:

From: Zi Yan ziy@nvidia.com

Huge pages in the process with the given pid and virtual address range are split. It is used to test split huge page function. In addition, a testing program is added to tools/testing/selftests/vm to utilize the interface by splitting PMD THPs.

Signed-off-by: Zi Yan ziy@nvidia.com

mm/huge_memory.c | 98 +++++++++++ mm/internal.h | 1 + mm/migrate.c | 2 +- tools/testing/selftests/vm/Makefile | 1 + .../selftests/vm/split_huge_page_test.c | 161 ++++++++++++++++++ 5 files changed, 262 insertions(+), 1 deletion(-) 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 207ebca8c654..c4fead5ead31 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> @@ -2935,10 +2936,107 @@ 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;
• nodemask_t task_nodes;
• struct mm_struct *mm;
• 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[80] = '\0';

Hm. Out-of-buffer access?

• ret = sscanf(input_buf, "%d,%lx,%lx", &pid, &vaddr_start, &vaddr_end);

Why hex without 0x prefix?

• 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);
  

• mm = find_mm_struct(pid, &task_nodes);

I don't follow why you need nodemask.

• if (IS_ERR(mm)) {

• ret = -EINVAL;
  

• goto out;
  

• }
• mmap_read_lock(mm);
• for (addr = vaddr_start; addr < vaddr_end;) {

• struct vm_area_struct *vma = find_vma(mm, addr);
  

• unsigned int follflags;
  

• struct page *page;
  

• if (!vma || addr < vma->vm_start || !vma_migratable(vma))
  

• 	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))
  

• 	goto next;
  

• if (!can_split_huge_page(page, NULL))
  

• 	goto next;
  

• if (!trylock_page(page))
  

• 	goto next;
  

• addr += page_size(page) - PAGE_SIZE;
  

Who said it was mapped as huge? mremap() allows to construct an PTE page table that filled with PTE-mapped THPs, each of them distinct.

• /* reset addr if split fails */
  

• if (split_huge_page(page))
  

• 	addr -= (page_size(page) - PAGE_SIZE);
  

• unlock_page(page);
  

+next:

• /* next page */
  

• addr += page_size(page);
  

Isn't it the second time if split_huge_page() succeed.

• put_page(page);
  

• }
• mmap_read_unlock(mm);
• mmput(mm);

+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/mm/internal.h b/mm/internal.h index 3ea43642b99d..fd841a38830f 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -624,4 +624,5 @@ struct migration_target_control { bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end); void page_cache_free_page(struct address_space *mapping, struct page *page); +struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes); #endif /* __MM_INTERNAL_H */ diff --git a/mm/migrate.c b/mm/migrate.c index a50bbb0e029b..e35654d1087d 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1851,7 +1851,7 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages, return nr_pages ? -EFAULT : 0; } -static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes) +struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes) { struct task_struct *task; struct mm_struct *mm; diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile index 62fb15f286ee..d9ead0cdd3e9 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 ($(ARCH),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..c8a32ae9e13a --- /dev/null +++ b/tools/testing/selftests/vm/split_huge_page_test.c @@ -0,0 +1,161 @@ +// SPDX-License-Identifier: GPL-2.0

+#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>

+#define PAGE_4KB (4096UL) +#define PAGE_2MB (512UL*PAGE_4KB) +#define PAGE_1GB (512UL*PAGE_2MB)

+#define PRESENT_MASK (1UL<<63) +#define SWAPPED_MASK (1UL<<62) +#define PAGE_TYPE_MASK (1UL<<61) +#define PFN_MASK ((1UL<<55)-1)

+#define KPF_THP (1UL<<22) +#define KPF_PUD_THP (1UL<<27)

+#define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages_in_range_pid" +#define SMAP_PATH "/proc/self/smaps" +#define INPUT_MAX 80

+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,%lx,%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, 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 * PAGE_2MB;
• uint64_t thp_size;
• one_page = memalign(PAGE_1GB, len);
• madvise(one_page, len, MADV_HUGEPAGE);
• memset(one_page, 1, len);
• thp_size = check_huge(one_page);
• if (!thp_size) {

• printf("No THP is allocatd");
  

• exit(EXIT_FAILURE);
  

• }
• /* split all possible huge pages */
• write_debugfs(getpid(), (uint64_t)one_page, (uint64_t)one_page + len);
• *one_page = 0;
• 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);

+}

+int main(int argc, char **argv) +{

• split_pmd_thp();
• return 0;

+}

2.28.0