ext4: re-enable extent zeroout optimization on encrypted files

From: Eric Biggers <[email protected]>

For encrypted files, commit 36086d43f657 ("ext4 crypto: fix bugs in ext4_encrypted_zeroout()") disabled the optimization where when a write occurs to the middle of an unwritten extent, the head and/or tail of the extent (when they aren't too large) are zeroed out, turned into an initialized extent, and merged with the part being written to. This optimization helps prevent fragmentation of the extent tree.

However, disabling this optimization also made fscrypt_zeroout_range() nearly impossible to test, as now it's only reachable via the very rare case in ext4_split_extent_at() where allocating a new extent tree block fails due to ENOSPC. 'gce-xfstests -c ext4/encrypt -g auto' doesn't even hit this at all.

It's preferable to avoid really rare cases that are hard to test.

That commit also cited data corruption in xfstest generic/127 as a reason to disable the extent zeroout optimization, but that's no longer reproducible anymore. It also cited fscrypt_zeroout_range() having poor performance, but I've written a patch to fix that.

Therefore, re-enable the extent zeroout optimization on encrypted files.

---
 fs/ext4/extents.c | 3 ---
 1 file changed, 3 deletions(-)

index dae66e8f0c3a..fee19c9f5fe3 100644
@@ -3718,9 +3718,6 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 		max_zeroout = sbi->s_extent_max_zeroout_kb >>
 			(inode->i_sb->s_blocksize_bits - 10);
 
-	if (IS_ENCRYPTED(inode))
-		max_zeroout = 0;
-
 	/*
 	 * five cases:
 	 * 1. split the extent into three extents.

2.24.1

Thanks, applied.

- Ted