[PATCH] btrfs: Use readahead_batch_length

[Matthew Wilcox (Oracle)]

Implement readahead_batch_length() to determine the number of bytes in
the current batch of readahead pages and use it in btrfs.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 fs/btrfs/extent_io.c    | 6 ++----
 include/linux/pagemap.h | 9 +++++++++
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index e9837562f7d6..97ac4ddb2857 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4875,10 +4875,8 @@ void extent_readahead(struct readahead_control *rac)
 	int nr;
 
 	while ((nr = readahead_page_batch(rac, pagepool))) {
-		u64 contig_start = page_offset(pagepool[0]);
-		u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1;
-
-		ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end);
+		u64 contig_start = readahead_pos(rac);
+		u64 contig_end = contig_start + readahead_batch_length(rac) - 1;
 
 		contiguous_readpages(pagepool, nr, contig_start, contig_end,
 				&em_cached, &bio, &bio_flags, &prev_em_start);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2cbfd4c36026..92939afd4944 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1174,6 +1174,15 @@ static inline unsigned int readahead_count(struct readahead_control *rac)
 	return rac->_nr_pages;
 }
 
+/**
+ * readahead_batch_length - The number of bytes in the current batch.
+ * @rac: The readahead request.
+ */
+static inline loff_t readahead_batch_length(struct readahead_control *rac)
+{
+	return rac->_batch_count * PAGE_SIZE;
+}
+
 static inline unsigned long dir_pages(struct inode *inode)
 {
 	return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >>
-- 
2.30.2