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

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

[Jan Prusakowski]

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.

Adjust the extent verification in generic/064 to expect exactly 50
extents on F2FS, while preserving the strict 1-extent requirement for
all other filesystems. Data integrity continues to be verified via byte
comparison.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Jan Prusakowski <jprusakowski@google.com>
---
 tests/generic/064 | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tests/generic/064 b/tests/generic/064
index aed13970..b77eccb4 100755
--- a/tests/generic/064
+++ b/tests/generic/064
@@ -59,7 +59,13 @@ for (( j=0; j < $(($BLOCKS/2)); j++ )); do
 done
 
 extent_after=`_count_extents $dest`
-if [ $extent_before -ne $extent_after ]; then
+
+if [ "$FSTYP" == "f2fs" ];
+then
+	if [ $extent_before -ne 1 ] || [ $extent_after -ne 50 ]; then
+		echo "extents mismatched before = $extent_before after = $extent_after"
+	fi
+elif [ $extent_before -ne $extent_after ]; then
 	echo "extents mismatched before = $extent_before after = $extent_after"
 fi
 
-- 
2.55.0.rc0.786.g65d90a0328-goog

Re: [f2fs-dev] [PATCH] generic/064: allow 50 extents on F2FS after fcollapse

[Chao Yu]

On 6/22/26 15:04, Jan Prusakowski via Linux-f2fs-devel 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.
> 
> Adjust the extent verification in generic/064 to expect exactly 50
> extents on F2FS, while preserving the strict 1-extent requirement for
> all other filesystems. Data integrity continues to be verified via byte
> comparison.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> Signed-off-by: Jan Prusakowski <jprusakowski@google.com>

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

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

[Christoph Hellwig]

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.

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

[Zorro Lang]

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?

> 

Re: [f2fs-dev] [PATCH] generic/064: allow 50 extents on F2FS after fcollapse

[Chao Yu]

On 6/30/26 00:37, Zorro Lang via Linux-f2fs-devel wrote:
> On Wed, Jun 24, 2026 at 12:46:01AM -0700, Christoph Hellwig wrote:
>> 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?

Hi Christoph, Zorro,

Let me explain it briefly, this is because f2fs has only one copy of reverse
mapping table (aka SSA), for any checkpointed data, we can not modify SSA info
directly during remap, otherwise, after sudden power-cut, we will suffer
inconsistent issue in between reverse mapping table and mapping table. So, f2fs
choose to rewrite for any checkpointed data.

Thanks,