[PATCH v2 12/18] mm/filemap: Move the iocb checks into filemap_update_page

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

We don't need to give up when a non-blocking request sees a !Uptodate page.
We may be able to satisfy the read from a partially-uptodate page.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
 mm/filemap.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 93c054f51677..9db94876122c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2236,17 +2236,18 @@ static int filemap_update_page(struct kiocb *iocb,
 		struct page *page, loff_t pos, loff_t count)
 {
 	struct inode *inode = mapping->host;
-	int error;
+	int error = -EAGAIN;
 
-	if (iocb->ki_flags & IOCB_WAITQ) {
-		error = lock_page_async(page, iocb->ki_waitq);
-		if (error)
+	if (!trylock_page(page)) {
+		if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO))
 			goto error;
-	} else {
-		if (!trylock_page(page)) {
+		if (!(iocb->ki_flags & IOCB_WAITQ)) {
 			put_and_wait_on_page_locked(page, TASK_KILLABLE);
 			return AOP_TRUNCATED_PAGE;
 		}
+		error = __lock_page_async(page, iocb->ki_waitq);
+		if (error)
+			goto error;
 	}
 
 	if (!page->mapping)
@@ -2368,14 +2369,9 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
 		}
 
 		if (!PageUptodate(page)) {
-			if ((iocb->ki_flags & IOCB_NOWAIT) ||
-			    ((iocb->ki_flags & IOCB_WAITQ) && pvec->nr > 1)) {
-				put_page(page);
-				pvec->nr--;
-				err = -EAGAIN;
-				goto err;
-			}
-
+			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);
 			if (err)
-- 
2.28.0