Unlike PAGE_SIZE == sectorsize case, read in subpage btrfs are always
merged if the range is in the same page:
E.g:
For regular sectorsize case, if we want to read range [0, 16K) of a
file, the bio will look like:
0 4K 8K 12K 16K
| bvec 1| bvec 2| bvec 3| bvec 4|
But for subpage case, above 16K can be merged into one bvec:
0 4K 8K 12K 16K
| bvec 1 |
This means our bvec is no longer 1:1 mapped to btrfs sector.
This makes repair much harder to do, if we want to do sector perfect
repair.
For now, just skip validation for subpage read repair, this means:
- We will submit extra range to repair
Even if we only have one sector error for above read, we will
still submit full 16K to over-write the bad copy
- Less chance to get good copy
Now the repair granularity is much lower, we need a copy with
all sectors correct to be able to submit a repair.
Sector perfect repair needs more modification, but for now the new
behavior should be good enough for us to test the basis of subpage
support.
Signed-off-by: Qu Wenruo <w...@suse.com>
---
fs/btrfs/extent_io.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 152aface4eeb..81931c02c0e4 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2651,6 +2651,19 @@ static bool btrfs_io_needs_validation(struct inode
*inode, struct bio *bio)
if (bio->bi_status == BLK_STS_OK)
return false;
+ /*
+ * For subpage case, read bio are always submitted as multiple-sector
+ * bio if the range is in the same page.
+ * For now, let's just skip the validation, and do page sized repair.
+ *
+ * This reduce the granularity for repair, meaning if we have two
+ * copies with different csum mismatch at different location, we're
+ * unable to repair in subpage case.
+ *
+ * TODO: Make validation code to be fully subpage compatible
+ */
+ if (blocksize < PAGE_SIZE)
+ return false;
/*
* We need to validate each sector individually if the failed I/O was
* for multiple sectors.
--
2.31.1
