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mm: huge_memory: debugfs for file-backed THP split
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Further extend <debugfs>/split_huge_pages to accept
"<path>,<pgoff_start>,<pgoff_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.

Link: https://lkml.kernel.org/r/20210331235309.332292-2-zi.yan@sent.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mika Penttila <mika.penttila@nextfour.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@x-y-z @torvalds
x-y-z authored and torvalds committed May 5, 2021
1 parent fa6c023 commit fbe3750
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Showing 2 changed files with 166 additions and 6 deletions.
90 changes: 89 additions & 1 deletion mm/huge_memory.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3050,14 +3050,74 @@ 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 index;
int nr_pages = 1;
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_debug("split file-backed THPs in file: %s, page offset: [0x%lx - 0x%lx]\n",
file_path, off_start, off_end);

mapping = candidate->f_mapping;

for (index = off_start; index < off_end; index += nr_pages) {
struct page *fpage = pagecache_get_page(mapping, index,
FGP_ENTRY | FGP_HEAD, 0);

nr_pages = 1;
if (xa_is_value(fpage) || !fpage)
continue;

if (!is_transparent_hugepage(fpage))
goto next;

total++;
nr_pages = thp_nr_pages(fpage);

if (!trylock_page(fpage))
goto next;

if (!split_huge_page(fpage))
split++;

unlock_page(fpage);
next:
put_page(fpage);
cond_resched();
}

filp_close(candidate, NULL);
ret = 0;

pr_debug("%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,
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 */
/* 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;

Expand All @@ -3072,6 +3132,34 @@ 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) {
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();
Expand Down
82 changes: 77 additions & 5 deletions tools/testing/selftests/vm/split_huge_page_test.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>

Expand All @@ -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)

Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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 */
Expand All @@ -300,6 +309,68 @@ 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];
uint64_t pgoff_start = 0, pgoff_end = 1024;

printf("Please enable pr_debug in split_huge_pages_in_file() if you need more info.\n");

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, pgoff_start, pgoff_end);

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) {
Expand All @@ -313,6 +384,7 @@ int main(int argc, char **argv)

split_pmd_thp();
split_pte_mapped_thp();
split_file_backed_thp();

return 0;
}

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