mm: huge_memory: debugfs for file-backed THP split

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>

1 files changed, 89 insertions, 1 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 58be9fc8253d..b3788683f7d3 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3050,6 +3050,65 @@ out:
 	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,
@@ -3057,7 +3116,8 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
 {
 	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;
 
@@ -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();