Re: [PATCH] btrfs: scrub: skip PREALLOC extents on RAID stripe-tree

[Johannes Thumshirn]

On 12.09.24 23:32, Qu Wenruo wrote:
> 
> 
> 在 2024/9/13 00:03, Johannes Thumshirn 写道:
>> From: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
>>
>> When scrubbing a RAID stripe-tree based filesystem with preallocated
>> extents, the btrfs_map_block() called by
>> scrub_submit_extent_sector_read() will return ENOENT, because there is
>> no RAID stripe-tree entry for preallocated extents. This then causes
>> the sector to be marked as a sector with an I/O error.
>>
>> To prevent this false alert don't mark secotors for that
>> btrfs_map_block() returned an ENOENT as I/O errors but skip them.
>>
>> This results for example in errors in fstests' btrfs/060 .. btrfs/074
>> which all perform fsstress and scrub operations. Whit this fix, these
>> errors are gone and the tests pass again.
>>
>> Cc: Qu Wenru <wqu@xxxxxxxx>
> 
> My concern is, ENOENT can be some real problems other than PREALLOC.
> I'd prefer this to be the last-resort method.

Hm but what else could create an entry in the extent tree without having 
it in the stripe tree? I can't really think of a situation creating this 
layout.


> Would it be possible to create an RST entry for preallocated operations
> manually? E.g. without creating a dummy OE, but just insert the needed
> RST entries into RST tree at fallocate time?

Let me give it a try. But I'm a bit less happy to do so, as RST already 
increases the write amplification.