[PATCHv6 15/22] thp, mm: naive support of thp in generic_perform_write

[Kirill A. Shutemov]

For now we still write/read at most PAGE_CACHE_SIZE bytes a time.

This implementation doesn't cover address spaces with backing storage.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/filemap.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 410879a801..38d6856737 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2384,12 +2384,14 @@ static ssize_t generic_perform_write(struct file *file,
 	if (segment_eq(get_fs(), KERNEL_DS))
 		flags |= AOP_FLAG_UNINTERRUPTIBLE;
 
+	i_split_down_read(mapping->host);
 	do {
 		struct page *page;
 		unsigned long offset;	/* Offset into pagecache page */
 		unsigned long bytes;	/* Bytes to write to page */
 		size_t copied;		/* Bytes copied from user */
 		void *fsdata;
+		int subpage_nr = 0;
 
 		offset = (pos & (PAGE_CACHE_SIZE - 1));
 		bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
@@ -2419,8 +2421,14 @@ again:
 		if (mapping_writably_mapped(mapping))
 			flush_dcache_page(page);
 
+		if (PageTransHuge(page)) {
+			off_t huge_offset = pos & ~HPAGE_PMD_MASK;
+			subpage_nr = huge_offset >> PAGE_CACHE_SHIFT;
+		}
+
 		pagefault_disable();
-		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
+		copied = iov_iter_copy_from_user_atomic(page + subpage_nr, i,
+				offset, bytes);
 		pagefault_enable();
 		flush_dcache_page(page);
 
@@ -2457,6 +2465,7 @@ again:
 		}
 	} while (iov_iter_count(i));
 
+	i_split_up_read(mapping->host);
 	return written ? written : status;
 }
 
-- 
1.8.4.rc3

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