Re: [PATCH] mm: huge_memory: a new debugfs interface for splitting THP tests.
From: David Hildenbrand
Date: Mon Mar 08 2021 - 13:12:12 EST
On 08.03.21 18:49, Zi Yan wrote:
On 8 Mar 2021, at 11:17, David Hildenbrand wrote:
On 08.03.21 16:22, 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.
Won't something like
1. MADV_HUGEPAGE
2. Access memory
3. MADV_NOHUGEPAGE
Have a similar effect? What's the benefit of this?
Thanks for checking the patch.
No, MADV_NOHUGEPAGE just replaces VM_HUGEPAGE with VM_NOHUGEPAGE,
nothing else will be done.
Ah, okay - maybe my memory was tricking me. There is some s390x KVM code
that forces MADV_NOHUGEPAGE and force-splits everything.
I do wonder, though, if this functionality would be worth a proper user
interface (e.g., madvise), though. There might be actual benefit in
having this as a !debug interface.
I think you aware of the discussion in
https://lkml.kernel.org/r/d098c392-273a-36a4-1a29-59731cdf5d3d@xxxxxxxxxx
If there will be an interface to collapse a THP -- "this memory area is
worth extra performance now by collapsing a THP if possible" -- it might
also be helpful to have the opposite functionality -- "this memory area
is not worth a THP, rather use that somehwere else".
MADV_HUGE_COLLAPSE vs. MADV_HUGE_SPLIT
Just a thought.
Without this, we do not have a way of splitting a specific THP
(the compound page) via any user interface for debugging.
We can only write to <debugfs>/split_huge_pages to split all THPs
in the system, which has an unwanted effect on the whole system
and can overwhelm us with a lot of information. This new debugfs
interface provides a more precise method.
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
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;
+}
--
Thanks,
David / dhildenb
—
Best Regards,
Yan Zi
--
Thanks,
David / dhildenb