From: Zi Yan <[email protected]>
We did 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. Make <debugfs>/split_huge_pages accept
a new command to do that.
By writing "<pid>,<vaddr_start>,<vaddr_end>" to
<debugfs>/split_huge_pages, THPs within the given virtual 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.
This does not change the old behavior, i.e., writing 1 to the interface
to split all THPs in the system.
Changelog:
From v5:
1. Skipped special VMAs and other fixes. (suggested by Yang Shi)
From v4:
1. Fixed the error code return issue, spotted by kernel test robot
<[email protected]>.
From v3:
1. Factored out split huge pages in the given pid code to a separate
function.
2. Added the missing put_page for not split pages.
3. pr_debug -> pr_info, make reading results simpler.
From v2:
1. Reused existing <debugfs>/split_huge_pages interface. (suggested by
Yang Shi)
From v1:
1. Removed unnecessary calling to vma_migratable, spotted by kernel test
robot <[email protected]>.
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 <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
---
mm/huge_memory.c | 151 ++++++++-
tools/testing/selftests/vm/.gitignore | 1 +
tools/testing/selftests/vm/Makefile | 1 +
.../selftests/vm/split_huge_page_test.c | 318 ++++++++++++++++++
4 files changed, 464 insertions(+), 7 deletions(-)
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..b653255a548e 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>
@@ -2922,16 +2923,14 @@ static struct shrinker deferred_split_shrinker = {
};
#ifdef CONFIG_DEBUG_FS
-static int split_huge_pages_set(void *data, u64 val)
+static void split_huge_pages_all(void)
{
struct zone *zone;
struct page *page;
unsigned long pfn, max_zone_pfn;
unsigned long total = 0, split = 0;
- if (val != 1)
- return -EINVAL;
-
+ pr_info("Split all THPs\n");
for_each_populated_zone(zone) {
max_zone_pfn = zone_end_pfn(zone);
for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
@@ -2959,11 +2958,149 @@ static int split_huge_pages_set(void *data, u64 val)
}
pr_info("%lu of %lu THP split\n", split, total);
+}
- return 0;
+static inline bool vma_not_suitable_for_thp_split(struct vm_area_struct *vma)
+{
+ return vma_is_special_huge(vma) || (vma->vm_flags & VM_IO) ||
+ is_vm_hugetlb_page(vma);
}
-DEFINE_DEBUGFS_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
- "%llu\n");
+
+static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
+ unsigned long vaddr_end)
+{
+ int ret = 0;
+ struct task_struct *task;
+ struct mm_struct *mm;
+ unsigned long total = 0, split = 0;
+ unsigned long addr;
+
+ vaddr_start &= PAGE_MASK;
+ vaddr_end &= PAGE_MASK;
+
+ /* 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;
+ }
+
+ pr_info("Split huge pages in pid: %d, vaddr: [0x%lx - 0x%lx]\n",
+ pid, vaddr_start, vaddr_end);
+
+ 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;
+
+ /* skip special VMA and hugetlb VMA */
+ if (vma_not_suitable_for_thp_split(vma)) {
+ addr = vma->vm_end;
+ continue;
+ }
+
+ /* FOLL_DUMP to ignore special (like zero) pages */
+ follflags = FOLL_GET | FOLL_DUMP;
+ page = follow_page(vma, addr, follflags);
+
+ if (IS_ERR(page))
+ continue;
+ if (!page)
+ continue;
+
+ if (!is_transparent_hugepage(page))
+ goto next;
+
+ total++;
+ if (!can_split_huge_page(compound_head(page), NULL))
+ goto next;
+
+ if (!trylock_page(page))
+ goto next;
+
+ if (!split_huge_page(page))
+ split++;
+
+ unlock_page(page);
+next:
+ put_page(page);
+ }
+ mmap_read_unlock(mm);
+ mmput(mm);
+
+ pr_info("%lu of %lu THP split\n", split, total);
+
+out:
+ return ret;
+}
+
+#define MAX_INPUT_BUF_SZ 255
+
+static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppops)
+{
+ static DEFINE_MUTEX(split_debug_mutex);
+ ssize_t ret;
+ char input_buf[MAX_INPUT_BUF_SZ]; /* hold pid, start_vaddr, end_vaddr */
+ int pid;
+ unsigned long vaddr_start, vaddr_end;
+
+ ret = mutex_lock_interruptible(&split_debug_mutex);
+ if (ret)
+ return ret;
+
+ ret = -EFAULT;
+
+ memset(input_buf, 0, MAX_INPUT_BUF_SZ);
+ if (copy_from_user(input_buf, buf, min_t(size_t, count, MAX_INPUT_BUF_SZ)))
+ goto out;
+
+ input_buf[MAX_INPUT_BUF_SZ - 1] = '\0';
+ ret = sscanf(input_buf, "%d,0x%lx,0x%lx", &pid, &vaddr_start, &vaddr_end);
+ if (ret == 1 && pid == 1) {
+ split_huge_pages_all();
+ ret = strlen(input_buf);
+ goto out;
+ } else if (ret != 3) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end);
+ if (!ret)
+ ret = strlen(input_buf);
+out:
+ mutex_unlock(&split_debug_mutex);
+ return ret;
+
+}
+
+static const struct file_operations split_huge_pages_fops = {
+ .owner = THIS_MODULE,
+ .write = split_huge_pages_write,
+ .llseek = no_llseek,
+};
static int __init split_huge_pages_debugfs(void)
{
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..2c0c18e60c57
--- /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 interface.
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <inttypes.h>
+#include <string.h>
+#include <fcntl.h>
+#include <sys/mman.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"
+#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);
+
+ if (!one_page) {
+ printf("Fail to allocate memory\n");
+ exit(EXIT_FAILURE);
+ }
+
+ 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 allocated\n");
+ 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 allocated\n");
+ 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;
+}
--
2.30.2
From: Zi Yan <[email protected]>
Further extend <debugfs>/split_huge_pages to accept
"<path>,<off_start>,<off_end>" for file-backed THP split tests since
tmpfs may have file backed by THP that mapped nowhere.
Update selftest program to test file-backed THP split too.
Suggested-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Zi Yan <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
---
mm/huge_memory.c | 91 ++++++++++++++++++-
.../selftests/vm/split_huge_page_test.c | 79 +++++++++++++++-
2 files changed, 164 insertions(+), 6 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b653255a548e..d3b20e101df2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3055,6 +3055,65 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
return ret;
}
+static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
+ pgoff_t off_end)
+{
+ struct filename *file;
+ struct file *candidate;
+ struct address_space *mapping;
+ int ret = -EINVAL;
+ pgoff_t off_cur;
+ unsigned long total = 0, split = 0;
+
+ file = getname_kernel(file_path);
+ if (IS_ERR(file))
+ return ret;
+
+ candidate = file_open_name(file, O_RDONLY, 0);
+ if (IS_ERR(candidate))
+ goto out;
+
+ pr_info("split file-backed THPs in file: %s, offset: [0x%lx - 0x%lx]\n",
+ file_path, off_start, off_end);
+
+ mapping = candidate->f_mapping;
+
+ for (off_cur = off_start; off_cur < off_end;) {
+ struct page *fpage = pagecache_get_page(mapping, off_cur,
+ FGP_ENTRY | FGP_HEAD, 0);
+
+ if (xa_is_value(fpage) || !fpage) {
+ off_cur += PAGE_SIZE;
+ continue;
+ }
+
+ if (!is_transparent_hugepage(fpage)) {
+ off_cur += PAGE_SIZE;
+ goto next;
+ }
+ total++;
+ off_cur = fpage->index + thp_size(fpage);
+
+ if (!trylock_page(fpage))
+ goto next;
+
+ if (!split_huge_page(fpage))
+ split++;
+
+ unlock_page(fpage);
+next:
+ put_page(fpage);
+ }
+
+ filp_close(candidate, NULL);
+ ret = 0;
+
+ pr_info("%lu of %lu file-backed THP split\n", split, total);
+out:
+ putname(file);
+ return ret;
+}
+
#define MAX_INPUT_BUF_SZ 255
static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
@@ -3062,7 +3121,8 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
{
static DEFINE_MUTEX(split_debug_mutex);
ssize_t ret;
- char input_buf[MAX_INPUT_BUF_SZ]; /* hold pid, start_vaddr, end_vaddr */
+ /* hold pid, start_vaddr, end_vaddr or file_path, off_start, off_end */
+ char input_buf[MAX_INPUT_BUF_SZ];
int pid;
unsigned long vaddr_start, vaddr_end;
@@ -3077,6 +3137,35 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
goto out;
input_buf[MAX_INPUT_BUF_SZ - 1] = '\0';
+
+ if (input_buf[0] == '/') {
+ char *tok;
+ char *buf = input_buf;
+ char file_path[MAX_INPUT_BUF_SZ];
+ pgoff_t off_start = 0, off_end = 0;
+ size_t input_len = strlen(input_buf);
+
+ tok = strsep(&buf, ",");
+ if (tok) {
+ strncpy(file_path, tok, MAX_INPUT_BUF_SZ);
+ } else {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ ret = sscanf(buf, "0x%lx,0x%lx", &off_start, &off_end);
+ if (ret != 2) {
+ pr_info("ret: %ld\n", ret);
+ ret = -EINVAL;
+ goto out;
+ }
+ ret = split_huge_pages_in_file(file_path, off_start, off_end);
+ if (!ret)
+ ret = input_len;
+
+ goto out;
+ }
+
ret = sscanf(input_buf, "%d,0x%lx,0x%lx", &pid, &vaddr_start, &vaddr_end);
if (ret == 1 && pid == 1) {
split_huge_pages_all();
diff --git a/tools/testing/selftests/vm/split_huge_page_test.c b/tools/testing/selftests/vm/split_huge_page_test.c
index 2c0c18e60c57..ebdf2d738978 100644
--- a/tools/testing/selftests/vm/split_huge_page_test.c
+++ b/tools/testing/selftests/vm/split_huge_page_test.c
@@ -7,11 +7,13 @@
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
+#include <stdarg.h>
#include <unistd.h>
#include <inttypes.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
+#include <sys/mount.h>
#include <malloc.h>
#include <stdbool.h>
@@ -24,6 +26,9 @@ uint64_t pmd_pagesize;
#define SMAP_PATH "/proc/self/smaps"
#define INPUT_MAX 80
+#define PID_FMT "%d,0x%lx,0x%lx"
+#define PATH_FMT "%s,0x%lx,0x%lx"
+
#define PFN_MASK ((1UL<<55)-1)
#define KPF_THP (1UL<<22)
@@ -87,13 +92,16 @@ static int write_file(const char *path, const char *buf, size_t buflen)
return (unsigned int) numwritten;
}
-static void write_debugfs(int pid, uint64_t vaddr_start, uint64_t vaddr_end)
+static void write_debugfs(const char *fmt, ...)
{
char input[INPUT_MAX];
int ret;
+ va_list argp;
+
+ va_start(argp, fmt);
+ ret = vsnprintf(input, INPUT_MAX, fmt, argp);
+ va_end(argp);
- 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);
@@ -183,7 +191,8 @@ void split_pmd_thp(void)
}
/* split all THPs */
- write_debugfs(getpid(), (uint64_t)one_page, (uint64_t)one_page + len);
+ write_debugfs(PID_FMT, getpid(), (uint64_t)one_page,
+ (uint64_t)one_page + len);
for (i = 0; i < len; i++)
if (one_page[i] != (char)i) {
@@ -274,7 +283,7 @@ void split_pte_mapped_thp(void)
}
/* split all remapped THPs */
- write_debugfs(getpid(), (uint64_t)pte_mapped,
+ write_debugfs(PID_FMT, getpid(), (uint64_t)pte_mapped,
(uint64_t)pte_mapped + pagesize * 4);
/* smap does not show THPs after mremap, use kpageflags instead */
@@ -300,6 +309,65 @@ void split_pte_mapped_thp(void)
close(kpageflags_fd);
}
+void split_file_backed_thp(void)
+{
+ int status;
+ int fd;
+ ssize_t num_written;
+ char tmpfs_template[] = "/tmp/thp_split_XXXXXX";
+ const char *tmpfs_loc = mkdtemp(tmpfs_template);
+ char testfile[INPUT_MAX];
+
+ status = mount("tmpfs", tmpfs_loc, "tmpfs", 0, "huge=always,size=4m");
+
+ if (status) {
+ printf("Unable to create a tmpfs for testing\n");
+ exit(EXIT_FAILURE);
+ }
+
+ status = snprintf(testfile, INPUT_MAX, "%s/thp_file", tmpfs_loc);
+ if (status >= INPUT_MAX) {
+ printf("Fail to create file-backed THP split testing file\n");
+ goto cleanup;
+ }
+
+ fd = open(testfile, O_CREAT|O_WRONLY);
+ if (fd == -1) {
+ perror("Cannot open testing file\n");
+ goto cleanup;
+ }
+
+ /* write something to the file, so a file-backed THP can be allocated */
+ num_written = write(fd, tmpfs_loc, sizeof(tmpfs_loc));
+ close(fd);
+
+ if (num_written < 1) {
+ printf("Fail to write data to testing file\n");
+ goto cleanup;
+ }
+
+ /* split the file-backed THP */
+ write_debugfs(PATH_FMT, testfile, 0, 1024);
+
+ status = unlink(testfile);
+ if (status)
+ perror("Cannot remove testing file\n");
+
+cleanup:
+ status = umount(tmpfs_loc);
+ if (status) {
+ printf("Unable to umount %s\n", tmpfs_loc);
+ exit(EXIT_FAILURE);
+ }
+ status = rmdir(tmpfs_loc);
+ if (status) {
+ perror("cannot remove tmp dir");
+ exit(EXIT_FAILURE);
+ }
+
+ printf("file-backed THP split test done, please check dmesg for more information\n");
+}
+
int main(int argc, char **argv)
{
if (geteuid() != 0) {
@@ -313,6 +381,7 @@ int main(int argc, char **argv)
split_pmd_thp();
split_pte_mapped_thp();
+ split_file_backed_thp();
return 0;
}
--
2.30.2
On Mon, 22 Mar 2021, Zi Yan wrote:
> From: Zi Yan <[email protected]>
>
> We did 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. Make <debugfs>/split_huge_pages accept
> a new command to do that.
>
> By writing "<pid>,<vaddr_start>,<vaddr_end>" to
> <debugfs>/split_huge_pages, THPs within the given virtual 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.
>
I'm curious if this is the only use case or whether you have additional
use cases or extensions in mind?
Specifically, I'm wondering if you are looking into more appropriately
dividing the limited number of hugepages available on the system amongst
the most latency sensitive processes?
The set of hugepages available on the system can be limited by
fragmentation. We've found opportunities where latency sensitive
processes would benefit from memory backed by thp, but they cannot be
allocated at fault for this reason. Yet, there are other processes that
have memory backed by hugepages that may not be benefiting from them.
Could this be useful to split a hugepage for a latency tolerant
application, migrate the pages elsewhere, and make the now-free hugepage
available for a latency sensitive application (through something like my
MADV_COLLAPSE proposal?)
Couple questions inline.
> This does not change the old behavior, i.e., writing 1 to the interface
> to split all THPs in the system.
>
> Changelog:
>
> From v5:
> 1. Skipped special VMAs and other fixes. (suggested by Yang Shi)
>
> From v4:
> 1. Fixed the error code return issue, spotted by kernel test robot
> <[email protected]>.
>
> From v3:
> 1. Factored out split huge pages in the given pid code to a separate
> function.
> 2. Added the missing put_page for not split pages.
> 3. pr_debug -> pr_info, make reading results simpler.
>
> From v2:
> 1. Reused existing <debugfs>/split_huge_pages interface. (suggested by
> Yang Shi)
>
> From v1:
> 1. Removed unnecessary calling to vma_migratable, spotted by kernel test
> robot <[email protected]>.
> 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 <[email protected]>
> Reviewed-by: Yang Shi <[email protected]>
> ---
> mm/huge_memory.c | 151 ++++++++-
> tools/testing/selftests/vm/.gitignore | 1 +
> tools/testing/selftests/vm/Makefile | 1 +
> .../selftests/vm/split_huge_page_test.c | 318 ++++++++++++++++++
> 4 files changed, 464 insertions(+), 7 deletions(-)
> 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..b653255a548e 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>
> @@ -2922,16 +2923,14 @@ static struct shrinker deferred_split_shrinker = {
> };
>
> #ifdef CONFIG_DEBUG_FS
> -static int split_huge_pages_set(void *data, u64 val)
> +static void split_huge_pages_all(void)
> {
> struct zone *zone;
> struct page *page;
> unsigned long pfn, max_zone_pfn;
> unsigned long total = 0, split = 0;
>
> - if (val != 1)
> - return -EINVAL;
> -
> + pr_info("Split all THPs\n");
Is this necessary to print?
> for_each_populated_zone(zone) {
> max_zone_pfn = zone_end_pfn(zone);
> for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
> @@ -2959,11 +2958,149 @@ static int split_huge_pages_set(void *data, u64 val)
> }
>
> pr_info("%lu of %lu THP split\n", split, total);
> +}
>
> - return 0;
> +static inline bool vma_not_suitable_for_thp_split(struct vm_area_struct *vma)
> +{
> + return vma_is_special_huge(vma) || (vma->vm_flags & VM_IO) ||
> + is_vm_hugetlb_page(vma);
> }
> -DEFINE_DEBUGFS_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
> - "%llu\n");
> +
> +static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
> + unsigned long vaddr_end)
> +{
> + int ret = 0;
> + struct task_struct *task;
> + struct mm_struct *mm;
> + unsigned long total = 0, split = 0;
> + unsigned long addr;
> +
> + vaddr_start &= PAGE_MASK;
> + vaddr_end &= PAGE_MASK;
> +
> + /* 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;
> + }
> +
> + pr_info("Split huge pages in pid: %d, vaddr: [0x%lx - 0x%lx]\n",
> + pid, vaddr_start, vaddr_end);
Hmm, does this need to be in the kernel log?
> +
> + 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;
> +
Should there be a cond_resched() right here?
> + /* skip special VMA and hugetlb VMA */
> + if (vma_not_suitable_for_thp_split(vma)) {
> + addr = vma->vm_end;
> + continue;
> + }
> +
> + /* FOLL_DUMP to ignore special (like zero) pages */
> + follflags = FOLL_GET | FOLL_DUMP;
> + page = follow_page(vma, addr, follflags);
> +
> + if (IS_ERR(page))
> + continue;
> + if (!page)
> + continue;
> +
> + if (!is_transparent_hugepage(page))
> + goto next;
> +
> + total++;
> + if (!can_split_huge_page(compound_head(page), NULL))
> + goto next;
> +
> + if (!trylock_page(page))
> + goto next;
> +
> + if (!split_huge_page(page))
> + split++;
> +
> + unlock_page(page);
> +next:
> + put_page(page);
> + }
> + mmap_read_unlock(mm);
> + mmput(mm);
> +
> + pr_info("%lu of %lu THP split\n", split, total);
> +
> +out:
> + return ret;
> +}
> +
> +#define MAX_INPUT_BUF_SZ 255
> +
> +static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
> + size_t count, loff_t *ppops)
> +{
> + static DEFINE_MUTEX(split_debug_mutex);
> + ssize_t ret;
> + char input_buf[MAX_INPUT_BUF_SZ]; /* hold pid, start_vaddr, end_vaddr */
> + int pid;
> + unsigned long vaddr_start, vaddr_end;
> +
> + ret = mutex_lock_interruptible(&split_debug_mutex);
> + if (ret)
> + return ret;
> +
> + ret = -EFAULT;
> +
> + memset(input_buf, 0, MAX_INPUT_BUF_SZ);
> + if (copy_from_user(input_buf, buf, min_t(size_t, count, MAX_INPUT_BUF_SZ)))
> + goto out;
> +
> + input_buf[MAX_INPUT_BUF_SZ - 1] = '\0';
> + ret = sscanf(input_buf, "%d,0x%lx,0x%lx", &pid, &vaddr_start, &vaddr_end);
> + if (ret == 1 && pid == 1) {
> + split_huge_pages_all();
> + ret = strlen(input_buf);
> + goto out;
> + } else if (ret != 3) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end);
> + if (!ret)
> + ret = strlen(input_buf);
> +out:
> + mutex_unlock(&split_debug_mutex);
> + return ret;
> +
> +}
> +
> +static const struct file_operations split_huge_pages_fops = {
> + .owner = THIS_MODULE,
> + .write = split_huge_pages_write,
> + .llseek = no_llseek,
> +};
>
> static int __init split_huge_pages_debugfs(void)
> {
On 24 Mar 2021, at 15:16, David Rientjes wrote:
> On Mon, 22 Mar 2021, Zi Yan wrote:
>
>> From: Zi Yan <[email protected]>
>>
>> We did 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. Make <debugfs>/split_huge_pages accept
>> a new command to do that.
>>
>> By writing "<pid>,<vaddr_start>,<vaddr_end>" to
>> <debugfs>/split_huge_pages, THPs within the given virtual 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.
>>
>
> I'm curious if this is the only use case or whether you have additional
> use cases or extensions in mind?
At the moment, this is the only use case I have in mind. I am developing
1GB THP support and split huge pages to any lower order (this will be useful
when Matthew Wilcox’s large page in page cache is in) and find there is no
way of splitting specific THPs (the compound pages) from user space.
So I added this interface for testing, mostly for splitting one or two
specified THPs. A potential extension might be to add a new <order>
parameter to test my split_huge_page_to_any_order(), after it gets in.
>
> Specifically, I'm wondering if you are looking into more appropriately
> dividing the limited number of hugepages available on the system amongst
> the most latency sensitive processes?
>
> The set of hugepages available on the system can be limited by
> fragmentation. We've found opportunities where latency sensitive
> processes would benefit from memory backed by thp, but they cannot be
> allocated at fault for this reason. Yet, there are other processes that
> have memory backed by hugepages that may not be benefiting from them.
>
> Could this be useful to split a hugepage for a latency tolerant
> application, migrate the pages elsewhere, and make the now-free hugepage
> available for a latency sensitive application (through something like my
> MADV_COLLAPSE proposal?)
The idea sounds quite interesting and reasonable. In the scenario you described,
I just wonder if we want to do SPLIT + COLLAPSE or we can combine them
into a single swap of THP and base pages (potentially using some extra free
pages as tmp space). Because there is no guarantee that the split subpages
can all be migrated and make space for a new THP, or other allocations might
steal a free page from the split THP range, causing subsequence THP allocation
failure.
I am OK with exposing this via a proper user space interface and can prepare
a patch for it. I just want to know if there are other use cases of splitting
THPs (the compound pages).
>
> Couple questions inline.
>
>> This does not change the old behavior, i.e., writing 1 to the interface
>> to split all THPs in the system.
>>
>> Changelog:
>>
>> From v5:
>> 1. Skipped special VMAs and other fixes. (suggested by Yang Shi)
>>
>> From v4:
>> 1. Fixed the error code return issue, spotted by kernel test robot
>> <[email protected]>.
>>
>> From v3:
>> 1. Factored out split huge pages in the given pid code to a separate
>> function.
>> 2. Added the missing put_page for not split pages.
>> 3. pr_debug -> pr_info, make reading results simpler.
>>
>> From v2:
>> 1. Reused existing <debugfs>/split_huge_pages interface. (suggested by
>> Yang Shi)
>>
>> From v1:
>> 1. Removed unnecessary calling to vma_migratable, spotted by kernel test
>> robot <[email protected]>.
>> 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 <[email protected]>
>> Reviewed-by: Yang Shi <[email protected]>
>> ---
>> mm/huge_memory.c | 151 ++++++++-
>> tools/testing/selftests/vm/.gitignore | 1 +
>> tools/testing/selftests/vm/Makefile | 1 +
>> .../selftests/vm/split_huge_page_test.c | 318 ++++++++++++++++++
>> 4 files changed, 464 insertions(+), 7 deletions(-)
>> 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..b653255a548e 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>
>> @@ -2922,16 +2923,14 @@ static struct shrinker deferred_split_shrinker = {
>> };
>>
>> #ifdef CONFIG_DEBUG_FS
>> -static int split_huge_pages_set(void *data, u64 val)
>> +static void split_huge_pages_all(void)
>> {
>> struct zone *zone;
>> struct page *page;
>> unsigned long pfn, max_zone_pfn;
>> unsigned long total = 0, split = 0;
>>
>> - if (val != 1)
>> - return -EINVAL;
>> -
>> + pr_info("Split all THPs\n");
>
> Is this necessary to print?
This interface accepts three different split commands, so I would like to explicitly
print what command is executed during my debugging.
>
>> for_each_populated_zone(zone) {
>> max_zone_pfn = zone_end_pfn(zone);
>> for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
>> @@ -2959,11 +2958,149 @@ static int split_huge_pages_set(void *data, u64 val)
>> }
>>
>> pr_info("%lu of %lu THP split\n", split, total);
>> +}
>>
>> - return 0;
>> +static inline bool vma_not_suitable_for_thp_split(struct vm_area_struct *vma)
>> +{
>> + return vma_is_special_huge(vma) || (vma->vm_flags & VM_IO) ||
>> + is_vm_hugetlb_page(vma);
>> }
>> -DEFINE_DEBUGFS_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
>> - "%llu\n");
>> +
>> +static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
>> + unsigned long vaddr_end)
>> +{
>> + int ret = 0;
>> + struct task_struct *task;
>> + struct mm_struct *mm;
>> + unsigned long total = 0, split = 0;
>> + unsigned long addr;
>> +
>> + vaddr_start &= PAGE_MASK;
>> + vaddr_end &= PAGE_MASK;
>> +
>> + /* 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;
>> + }
>> +
>> + pr_info("Split huge pages in pid: %d, vaddr: [0x%lx - 0x%lx]\n",
>> + pid, vaddr_start, vaddr_end);
>
> Hmm, does this need to be in the kernel log?
Since this is a debugfs interface, I expect it is only used for debugging,
which should be rare. pr_info would save us from the additional enabling
dynamic debug printing.
>
>> +
>> + 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;
>> +
>
> Should there be a cond_resched() right here?
I did not expect we are going to use this to split a lot of pages.
But I will add one here in case someone uses it that way.
>
>> + /* skip special VMA and hugetlb VMA */
>> + if (vma_not_suitable_for_thp_split(vma)) {
>> + addr = vma->vm_end;
>> + continue;
>> + }
>> +
>> + /* FOLL_DUMP to ignore special (like zero) pages */
>> + follflags = FOLL_GET | FOLL_DUMP;
>> + page = follow_page(vma, addr, follflags);
>> +
>> + if (IS_ERR(page))
>> + continue;
>> + if (!page)
>> + continue;
>> +
>> + if (!is_transparent_hugepage(page))
>> + goto next;
>> +
>> + total++;
>> + if (!can_split_huge_page(compound_head(page), NULL))
>> + goto next;
>> +
>> + if (!trylock_page(page))
>> + goto next;
>> +
>> + if (!split_huge_page(page))
>> + split++;
>> +
>> + unlock_page(page);
>> +next:
>> + put_page(page);
>> + }
>> + mmap_read_unlock(mm);
>> + mmput(mm);
>> +
>> + pr_info("%lu of %lu THP split\n", split, total);
>> +
>> +out:
>> + return ret;
>> +}
>> +
>> +#define MAX_INPUT_BUF_SZ 255
>> +
>> +static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
>> + size_t count, loff_t *ppops)
>> +{
>> + static DEFINE_MUTEX(split_debug_mutex);
>> + ssize_t ret;
>> + char input_buf[MAX_INPUT_BUF_SZ]; /* hold pid, start_vaddr, end_vaddr */
>> + int pid;
>> + unsigned long vaddr_start, vaddr_end;
>> +
>> + ret = mutex_lock_interruptible(&split_debug_mutex);
>> + if (ret)
>> + return ret;
>> +
>> + ret = -EFAULT;
>> +
>> + memset(input_buf, 0, MAX_INPUT_BUF_SZ);
>> + if (copy_from_user(input_buf, buf, min_t(size_t, count, MAX_INPUT_BUF_SZ)))
>> + goto out;
>> +
>> + input_buf[MAX_INPUT_BUF_SZ - 1] = '\0';
>> + ret = sscanf(input_buf, "%d,0x%lx,0x%lx", &pid, &vaddr_start, &vaddr_end);
>> + if (ret == 1 && pid == 1) {
>> + split_huge_pages_all();
>> + ret = strlen(input_buf);
>> + goto out;
>> + } else if (ret != 3) {
>> + ret = -EINVAL;
>> + goto out;
>> + }
>> +
>> + ret = split_huge_pages_pid(pid, vaddr_start, vaddr_end);
>> + if (!ret)
>> + ret = strlen(input_buf);
>> +out:
>> + mutex_unlock(&split_debug_mutex);
>> + return ret;
>> +
>> +}
>> +
>> +static const struct file_operations split_huge_pages_fops = {
>> + .owner = THIS_MODULE,
>> + .write = split_huge_pages_write,
>> + .llseek = no_llseek,
>> +};
>>
>> static int __init split_huge_pages_debugfs(void)
>> {
—
Best Regards,
Yan Zi