[PATCH v2 16/25] iomap: Support large pages in read paths

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

Use thp_size() instead of PAGE_SIZE, use offset_in_this_page() and
abstract away how to access the list of readahead pages.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 fs/iomap/buffered-io.c | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index e522039f627f..68f8903ecd6d 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -179,14 +179,16 @@ iomap_read_finish(struct iomap_page *iop, struct page *page)
 static void
 iomap_read_page_end_io(struct bio_vec *bvec, int error)
 {
-	struct page *page = bvec->bv_page;
+	struct page *page = compound_head(bvec->bv_page);
 	struct iomap_page *iop = to_iomap_page(page);
+	unsigned offset = bvec->bv_offset +
+				PAGE_SIZE * (bvec->bv_page - page);
 
 	if (unlikely(error)) {
 		ClearPageUptodate(page);
 		SetPageError(page);
 	} else {
-		iomap_set_range_uptodate(page, bvec->bv_offset, bvec->bv_len);
+		iomap_set_range_uptodate(page, offset, bvec->bv_len);
 	}
 
 	iomap_read_finish(iop, page);
@@ -239,6 +241,16 @@ 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)
@@ -263,7 +275,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		goto done;
 
 	if (iomap_block_needs_zeroing(inode, iomap, pos)) {
-		zero_user(page, poff, plen);
+		zero_user_large(page, poff, plen);
 		iomap_set_range_uptodate(page, poff, plen);
 		goto done;
 	}
@@ -294,7 +306,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 
 	if (!ctx->bio || !is_contig || bio_full(ctx->bio, plen)) {
 		gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
-		int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		int nr_vecs = iomap_nr_vecs(page, length);
 
 		if (ctx->bio)
 			submit_bio(ctx->bio);
@@ -331,9 +343,9 @@ iomap_readpage(struct page *page, const struct iomap_ops *ops)
 
 	trace_iomap_readpage(page->mapping->host, 1);
 
-	for (poff = 0; poff < PAGE_SIZE; poff += ret) {
-		ret = iomap_apply(inode, page_offset(page) + poff,
-				PAGE_SIZE - poff, 0, ops, &ctx,
+	for (poff = 0; poff < thp_size(page); poff += ret) {
+		ret = iomap_apply(inode, file_offset_of_page(page) + poff,
+				thp_size(page) - poff, 0, ops, &ctx,
 				iomap_readpage_actor);
 		if (ret <= 0) {
 			WARN_ON_ONCE(ret == 0);
@@ -376,7 +388,7 @@ iomap_readahead_actor(struct inode *inode, loff_t pos, loff_t length,
 		if (WARN_ON(ret == 0))
 			break;
 		done += ret;
-		if (offset_in_page(pos + done) == 0) {
+		if (offset_in_this_page(ctx->cur_page, pos + done) == 0) {
 			ctx->rac->nr_pages -= ctx->rac->batch_count;
 			if (!ctx->cur_page_in_bio)
 				unlock_page(ctx->cur_page);
-- 
2.25.0