Re: [PATCH] mm: huge_memory: a new debugfs interface for splitting THP tests.
From: Zi Yan
Date: Mon Mar 08 2021 - 13:47:45 EST
+ 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@xxxxxxxxxx>
>>>
>>> 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@xxxxxxxxxx>
>>
>> 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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