mm: huge_memory: a new debugfs interface for splitting THP tests
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.
Link: https://lkml.kernel.org/r/20210331235309.332292-1-zi.yan@sent.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mika Penttila <mika.penttila@nextfour.com>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9b31ef8..58be9fc 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>
@@ -2915,16 +2916,14 @@ 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_debug("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++) {
@@ -2948,15 +2947,155 @@ static int split_huge_pages_set(void *data, u64 val)
unlock_page(page);
next:
put_page(page);
+ cond_resched();
}
}
- pr_info("%lu of %lu THP split\n", split, total);
-
- return 0;
+ pr_debug("%lu of %lu THP split\n", split, total);
}
-DEFINE_DEBUGFS_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
- "%llu\n");
+
+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);
+}
+
+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_debug("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);
+ cond_resched();
+ }
+ mmap_read_unlock(mm);
+ mmput(mm);
+
+ pr_debug("%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)
{
