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btrfs: disable compressed readahead for subpage 

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>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2021-07-26 14:34:52 +08:00 committed by David Sterba
parent 3670e6451b
commit ca62e85ded
1 changed files with 10 additions and 0 deletions
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10
fs/btrfs/compression.c
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@ -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 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) {