Re: [PATCH] mm: huge_memory: a new debugfs interface for splitting THP tests.

From: Zi Yan
Date: Mon Mar 08 2021 - 14:02:47 EST

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In reply to: David Hildenbrand: "Re: [PATCH] mm: huge_memory: a new debugfs interface for splitting THP tests."
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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@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

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@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

—
Best Regards,
Yan Zi

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