[PATCH 08/14] iomap: Support THPs in readahead

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Use offset_in_thp() instead of offset_in_page() and change how we estimate
the number of bio_vecs we're going to need.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/iomap/buffered-io.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index ca305fbaf811..4ef02afaedc5 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -264,6 +264,16 @@ static inline bool iomap_block_needs_zeroing(struct inode *inode,
 		pos >= i_size_read(inode);
 }
 
+/*
+ * Estimate the number of vectors we need based on the current page size;
+ * if we're wrong we'll end up doing an overly large allocation or needing
+ * to do a second allocation, neither of which is a big deal.
+ */
+static unsigned int iomap_nr_vecs(struct page *page, loff_t length)
+{
+	return (length + thp_size(page) - 1) >> page_shift(page);
+}
+
 static loff_t
 iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		struct iomap *iomap, struct iomap *srcmap)
@@ -309,7 +319,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 	if (!is_contig || bio_full(ctx->bio, plen)) {
 		gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
 		gfp_t orig_gfp = gfp;
-		int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		int nr_vecs = iomap_nr_vecs(page, length);
 
 		if (ctx->bio)
 			submit_bio(ctx->bio);
@@ -424,7 +434,8 @@ iomap_readahead_actor(struct inode *inode, loff_t pos, loff_t length,
 	loff_t done, ret;
 
 	for (done = 0; done < length; done += ret) {
-		if (ctx->cur_page && offset_in_page(pos + done) == 0) {
+		if (ctx->cur_page &&
+		    offset_in_thp(ctx->cur_page, pos + done) == 0) {
 			if (!ctx->cur_page_in_bio)
 				unlock_page(ctx->cur_page);
 			put_page(ctx->cur_page);
-- 
2.28.0