[PATCH 06/12] mm, thp, tmpfs: initial support for huge page in write_begin/write_end in tmpfs

[Ning Qu <quning@google.com>]

For now we try to grab a huge cache page if the minimum requirements have been
satisfied.

Signed-off-by: Ning Qu <quning@gmail.com>
---
 mm/shmem.c | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 2fc450d..0a423a9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1640,8 +1640,21 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
 	struct inode *inode = mapping->host;
 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 	gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
+	int ret = 0;
+	int getpage_flags = 0;
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
+	/*
+	 * Do not allocate a huge page in the first huge page range in page
+	 * cache. This way we can avoid most small files overhead.
+	 */
+	if (pos >= HPAGE_PMD_SIZE)
+		getpage_flags |= AOP_FLAG_TRANSHUGE;
+#endif
+	ret = shmem_getpage(inode, index, pagep, SGP_WRITE, gfp,
+				getpage_flags, NULL);
 
-	return shmem_getpage(inode, index, pagep, SGP_WRITE, gfp, 0, NULL);
+	return ret;
 }
 
 static int
@@ -1655,10 +1668,18 @@ shmem_write_end(struct file *file, struct address_space *mapping,
 		i_size_write(inode, pos + copied);
 
 	if (!PageUptodate(page)) {
-		if (copied < PAGE_CACHE_SIZE) {
-			unsigned from = pos & (PAGE_CACHE_SIZE - 1);
-			zero_user_segments(page, 0, from,
-					from + copied, PAGE_CACHE_SIZE);
+		if (copied < len) {
+			unsigned from;
+			if (PageTransHugeCache(page)) {
+				from = pos & ~HPAGE_PMD_MASK;
+				zero_huge_user(page, 0, from);
+				zero_huge_user(page, from + copied,
+					       HPAGE_PMD_SIZE);
+			} else {
+				from = pos & ~PAGE_CACHE_MASK;
+				zero_user_segments(page, 0, from,
+						from + copied, PAGE_CACHE_SIZE);
+			}
 		}
 		SetPageUptodate(page);
 	}
-- 
1.8.4


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