On 8 Mar 2021, at 13:11, David Hildenbrand wrote:
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@nvidia.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.
Won't something like
MADV_HUGEPAGE
Access memory
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@google.com
Yes. Thanks for bringing this up.
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
I agree that MADV_HUGE_SPLIT would be useful as the opposite of COLLAPSE when user might just want PAGESIZE mappings. Right now, HUGE_SPLIT is implicit from mapping changes like mprotect or MADV_DONTNEED.
My debugfs interface is a little different here, since it splits the compound pages mapped by the PMD mapping (of course the PMD mapping is split too), whereas madvise only splits the PMD. I did not put it in a !debug interface because I do not think we want to expose the kernel mechanism (the compound page) to the user and let them decide when to split the compound page or not. MADV_HUGE_COLLAPSE is different, because we need to form a compound THP to be able to get PMD mappings. But I am happy to change my mind if we find usefulness in letting user split compound THPs via !debug interface.
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@nvidia.com
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,
return 0; } late_initcall(split_huge_pages_debugfs);&split_huge_pages_in_range_pid_fops);
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
— Best Regards, Yan Zi