Hi,
Recent btrfs/137 test case makes me wonder what's the designed behavior
of btrfs inline data extent.
The current behavior in fact is quite a chaos.
We need a standard of how inline extent should behave.
1) max_inline limit
The problem of current max_inline is, it's never clear what it is
limiting.
For example, we don't allow page sized inline extent if not
compressed.
But we allow page sized inline extent if it's compressed.
Is it just limiting size after compression?
What if we really want to limit size before compression?
2) inline extent condition
Is inline extent allowed if we have following regular extent?
For plain extent, prealloc can cause regular extent to co-exist with
inlined one.
While normal write will only convert inlined extent to regular one.
While for compressed extent, it can co-exist with regular extent, by
# xfs_io -f -c "pwrite 0 4k" -c sync -c "pwrite 4k 16k" /mnt/btrfs/file
So which is the correct behavior?
Personally I think we should not allow co-exist, as it's already
causing a lot of fixes for it, that's to say neither current
behavior is correct.
3) inline extent and fallocate
For inline extent, as long as we are calling fallocate inside the
page size, only the isize is expanded.
Only beyond page size, we get prealloc extents.
(However inlined extent is still here, not converted)
What's the designed behavior? Convert inline to regular or just
leave it as is?
Thanks,
Qu
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