Re: [PATCH] generic/064: allow 50 extents on F2FS after fcollapse

[Zorro Lang <zlang@kernel.org>]

On Wed, Jun 24, 2026 at 12:46:01AM -0700, Christoph Hellwig wrote:
> On Mon, Jun 22, 2026 at 07:04:38AM +0000, Jan Prusakowski wrote:
> > On F2FS, generic/064 fails with "extents mismatched before = 1 after =
> > 50" following multiple fcollapse (collapse range) operations.
> > 
> > To ensure crash consistency and checkpoint integrity, F2FS forbids
> > in-place SSR (Summary Standalone Replacement) overwrites on valid
> > checkpointed blocks. When collapse range shifts blocks, F2FS allocates
> > new data pages in LFS mode (out-of-place log writes). As a result,
> > sequential collapse range calls rewrite shifted blocks at new log
> > locations, intentionally leaving the file with 50 extents.
> 
> This sounds odd.  The test allocates a contigous range and then just does
> insert/collapse on it, which should not lead to any new data block
> allocations.  Given that the test works fine on zoned XFS and btrfs
> with strict out of place write policies we know it does not require
> overwriting blocks to work as well.
> 
> So I think something is fishy in f2fs if needs to allocate data blocks
> here.

I have the same question with Christoph. Shouldn't fcollapse in F2FS just
remap the metadata instead of allocating new data blocks?

>