Message-ID: <B307F250-3872-4AFA-9D43-5DD6144C039C@nvidia.com>
Date:   Mon, 08 Mar 2021 13:46:42 -0500
From:   "Zi Yan" <ziy@...dia.com>
To:     "Mika Penttilä" <mika.penttila@...tfour.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Shuah Khan" <shuah@...nel.org>,
        "John Hubbard" <jhubbard@...dia.com>,
        "Sandipan Das" <sandipan@...ux.ibm.com>
Subject: Re: [PATCH] mm: huge_memory: a new debugfs interface for splitting
 THP tests.

+ the rest of cc back and move your reply inline.

On 8 Mar 2021, at 12:47, Mika Penttilä wrote:
>>
>>
>> On 8.3.2021 17.22, Zi Yan wrote:
>>> From: Zi Yan <ziy@...dia.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@...dia.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.


>>
>>
>>> ---
>>>   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

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