[PATCH v7 03/17] btrfs: disable compressed readahead for subpage

[Qu Wenruo <wqu@suse.com>]

For current subpage support, we only support 64K page size with 4K
sector size.

This makes compressed readahead less effective, as maximum compressed
extent size is only 128K, 2x the page size.

On the other hand, the function add_ra_bio_pages() is still assuming
sectorsize == PAGE_SIZE, and code change may affect 4K page size
systems.

So for now, let's disable subpage compressed readahead for now.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index d40c2c878c83..f17be6398d2c 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -564,6 +564,16 @@ static noinline int add_ra_bio_pages(struct inode *inode,
 	if (isize == 0)
 		return 0;
 
+	/*
+	 * For current subpage support, we only support 64K page size,
+	 * which means maximum compressed extent size (128K) is just 2x page
+	 * size.
+	 * This makes readahead less effective, so here disable readahead for
+	 * subpage support for now, until full compressed write is supported.
+	 */
+	if (btrfs_sb(inode->i_sb)->sectorsize < PAGE_SIZE)
+		return 0;
+
 	end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
 
 	while (last_offset < compressed_end) {
-- 
2.32.0