Re: [PATCH] mm: huge_memory: a new debugfs interface for splitting THP tests. - Linux-kselftest-mirror

8 Mar 2021

+ the rest of cc back and move your reply inline.
On 8 Mar 2021, at 12:47, Mika Penttilä wrote:
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On 8.3.2021 17.22, Zi Yan wrote:
...
From: Zi Yan ziy@nvidia.com
By writing "<pid>,<vaddr_start>,<vaddr_end>" to
<debugfs>/split_huge_pages_in_range_pid, THPs 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 selftest program is added to
tools/testing/selftests/vm to utilize the interface by splitting
PMD THPs and PTE-mapped THPs.
Signed-off-by: Zi Yan ziy@nvidia.com
Hi!
I think your test program is not correct. The mremaps shrink to one page, after the first mremap the pointers are bogus.
Also, mremap splits pmds with split_huge_pmd().. And those you can't split  with split_huge_page because it is a normal pmd.
Maybe you didn't indent to shrink to page size?
--Mika
Hi,
Sorry, wrote too fast.. the splits are okay of course from pte mapped thp to plain pages (mremap -> split pmd -> debugfs write ->split pages).
But the remap offsets are I think maybe not you wanted.
You mean I mremap the first PAGESIZE from first THP, second PAGESIZE from second THP and so on to
create PTE-mapped THPs? I did it on purpose so split_huge_page can work on different part of THPs.
...
...
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mm/huge_memory.c                              |  98 ++++++
  mm/internal.h                                 |   1 +
  mm/migrate.c                                  |   2 +-
  tools/testing/selftests/vm/.gitignore         |   1 +
  tools/testing/selftests/vm/Makefile           |   1 +
  .../selftests/vm/split_huge_page_test.c       | 318 ++++++++++++++++++
  6 files changed, 420 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 395c75111d33..818172f887bf 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>
@@ -2971,10 +2972,107 @@ 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;
+    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);



+    mm = find_mm_struct(pid, &task_nodes);
+    if (IS_ERR(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 || !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))
+            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/mm/internal.h b/mm/internal.h
index 9902648f2206..1659d00100ef 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -623,4 +623,5 @@ struct migration_target_control {
      gfp_t gfp_mask;
  };
  +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 62b81d5257aa..ce5f213debb2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1913,7 +1913,7 @@ 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/.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..8ea8000fda62
--- /dev/null
+++ b/tools/testing/selftests/vm/split_huge_page_test.c
@@ -0,0 +1,318 @@
+// 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 possible huge pages */
+    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);
+    }



+    pte_mapped = mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE);



+    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 possible huge pages */
+    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;
+}
—
Best Regards,
Yan Zi

    