mm/filemap: add filemap_range_uptodate

Move the complicated condition and the calculations out of
filemap_update_page() into its own function.

[willy@infradead.org: unlock page before dropping its refcount]
  Link: https://lkml.kernel.org/r/20210201125229.GO308988@casper.infradead.org

Link: https://lkml.kernel.org/r/20210122160140.223228-14-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -2233,11 +2233,36 @@ static int filemap_read_page(struct file *file, struct address_space *mapping,
 	return error;
 }
 
+static bool filemap_range_uptodate(struct address_space *mapping,
+		loff_t pos, struct iov_iter *iter, struct page *page)
+{
+	int count;
+
+	if (PageUptodate(page))
+		return true;
+	/* pipes can't handle partially uptodate pages */
+	if (iov_iter_is_pipe(iter))
+		return false;
+	if (!mapping->a_ops->is_partially_uptodate)
+		return false;
+	if (mapping->host->i_blkbits >= (PAGE_SHIFT + thp_order(page)))
+		return false;
+
+	count = iter->count;
+	if (page_offset(page) > pos) {
+		count -= page_offset(page) - pos;
+		pos = 0;
+	} else {
+		pos -= page_offset(page);
+	}
+
+	return mapping->a_ops->is_partially_uptodate(page, pos, count);
+}
+
 static int filemap_update_page(struct kiocb *iocb,
 		struct address_space *mapping, struct iov_iter *iter,
-		struct page *page, loff_t pos, loff_t count)
+		struct page *page)
 {
-	struct inode *inode = mapping->host;
 	int error;
 
 	if (!trylock_page(page)) {
@@ -2254,26 +2279,15 @@ static int filemap_update_page(struct kiocb *iocb,
 
 	if (!page->mapping)
 		goto truncated;
-	if (PageUptodate(page))
-		goto uptodate;
-	if (inode->i_blkbits == PAGE_SHIFT ||
-			!mapping->a_ops->is_partially_uptodate)
-		goto readpage;
-	/* pipes can't handle partially uptodate pages */
-	if (unlikely(iov_iter_is_pipe(iter)))
-		goto readpage;
-	if (!mapping->a_ops->is_partially_uptodate(page,
-				pos & (thp_size(page) - 1), count))
-		goto readpage;
-uptodate:
-	unlock_page(page);
-	return 0;
 
-readpage:
-	if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ)) {
-		unlock_page(page);
-		return -EAGAIN;
-	}
+	error = 0;
+	if (filemap_range_uptodate(mapping, iocb->ki_pos, iter, page))
+		goto unlock;
+
+	error = -EAGAIN;
+	if (iocb->ki_flags & (IOCB_NOIO | IOCB_NOWAIT | IOCB_WAITQ))
+		goto unlock;
+
 	error = filemap_read_page(iocb->ki_filp, mapping, page);
 	if (error == AOP_TRUNCATED_PAGE)
 		put_page(page);
@@ -2282,6 +2296,9 @@ static int filemap_update_page(struct kiocb *iocb,
 	unlock_page(page);
 	put_page(page);
 	return AOP_TRUNCATED_PAGE;
+unlock:
+	unlock_page(page);
+	return error;
 }
 
 static int filemap_create_page(struct file *file,
@@ -2351,9 +2368,6 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
 	{
 		struct page *page = pvec->pages[pvec->nr - 1];
 		pgoff_t pg_index = page->index;
-		loff_t pg_pos = max(iocb->ki_pos,
-				    (loff_t) pg_index << PAGE_SHIFT);
-		loff_t pg_count = iocb->ki_pos + iter->count - pg_pos;
 
 		if (PageReadahead(page)) {
 			if (iocb->ki_flags & IOCB_NOIO) {
@@ -2370,8 +2384,7 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
 			if ((iocb->ki_flags & IOCB_WAITQ) &&
 			    pagevec_count(pvec) > 1)
 				iocb->ki_flags |= IOCB_NOWAIT;
-			err = filemap_update_page(iocb, mapping, iter, page,
-					pg_pos, pg_count);
+			err = filemap_update_page(iocb, mapping, iter, page);
 			if (err) {
 				if (err < 0)
 					put_page(page);