Re: [PATCH 1/4] generic/371: Fix the test to be compatible block sizes upto 64k

["Nirjhar Roy (IBM)" <nirjhar.roy.lists@gmail.com>]

On 9/26/25 22:07, Zorro Lang wrote:
> On Tue, Sep 16, 2025 at 03:30:09PM +0000, Nirjhar Roy (IBM) wrote:
>> When this test was ran with btrfs with 64k sector/block size, it
>> failed with
>>
>>       QA output created by 371
>>       Silence is golden
>>      +fallocate: No space left on device
>>      +pwrite: No space left on device
>>      +fallocate: No space left on device
>>      +pwrite: No space left on device
>>      +pwrite: No space left on device
>>      ...
>>
>> This is what is going on:
>>
>> Let us see the following set of operations:
>>
>> --- With 4k sector size ---
>> $ mkfs.btrfs -f -b 256m -s 4k -n 4k /dev/loop0
>> $ mount /dev/loop0 /mnt1/scratch/
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M  1.5M  175M   1% /mnt1/scratch
>>
>> $ xfs_io -f -c "pwrite 0 80M" /mnt1/scratch/t1
>> wrote 83886080/83886080 bytes at offset 0
>> 80 MiB, 20480 ops; 0.4378 sec (182.693 MiB/sec and 46769.3095 ops/sec)
>>
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M  1.5M  175M   1% /mnt1/scratch
>>
>> $ sync
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M   82M   95M  47% /mnt1/scratch
>>
>> $ xfs_io -f -c "pwrite 0 80M" /mnt1/scratch/t2
>> wrote 83886080/83886080 bytes at offset 0
>> 80 MiB, 20480 ops; 0:00:01.25 (63.881 MiB/sec and 16353.4648 ops/sec)
>>
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M  137M   40M  78% /mnt1/scratch
>>
>> $ sync
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M  162M   15M  92% /mnt1/scratch
>>
>> Now let us repeat with 64k sector size
>> --- With 64k sector size ---
>> $ mkfs.btrfs -f -b 256m -s 64k -n 64k /dev/loop0
>> $ mount /dev/loop0 /mnt1/scratch/
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M   24M  175M  12% /mnt1/scratch
>>
>> $ xfs_io -f -c "pwrite 0 80M" /mnt1/scratch/t1
>> wrote 83886080/83886080 bytes at offset 0
>> 80 MiB, 20480 ops; 0.8460 sec (94.553 MiB/sec and 24205.4914 ops/sec)
>> $
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M   24M  175M  12% /mnt1/scratch
>>
>> $ sync
>> $ df -h /dev/loop0
>> Filesystem      Size  Used Avail Use% Mounted on
>> /dev/loop0      256M  104M   95M  53% /mnt1/scratch
>>
>> $ xfs_io -f -c "pwrite 0 80M" /mnt1/scratch/t2
>> pwrite: No space left on device
>>
>> Now, we can see that with 64k node size, 256M is not sufficient
>> to hold 2 files worth 80M. For 64k, we can also see that the initial
>> space usage on a fresh filesystem is 24M and for 4k its 1.5M. So
>> because of higher node size, more metadata space is getting used.
>> This test requires the size of the filesystem to be at least capable
>> to hold 2 80M files.
>> Fix this by increasing the fs size from 256M to 330M.
> Thanks for this detailed explanation. As this's a ENOSPC test, so we
> must make sure this case still can uncover the original bug, before
> increasing the fs size. Can you make sure that? Or maybe we can replace
> that "80M" with a variable (according to "Avail" size).
Hi Filipe, Zorro

The original commit message of generic/371 says that this test catches 
some excess space usage issues. Is(Are) there any patch(es) that fix 
this issue - so that I can remove the commits and check if the test 
expectedly fails with slightly large fssize i.e, 330M?

I did find some related commits [1] and I ran the test with 330M and 
256M(the default size) after removing the commits[1] but the test passes 
with both the filesystem sizes. So I am guessing, this is not the patch 
that can test generic/371.

[1] 
https://lore.kernel.org/linux-btrfs/cover.1610747242.git.josef@toxicpanda.com/ 


--NR
>
> Thanks,
> Zorro
>
>> Reported-by: Disha Goel <disgoel@linux.ibm.com>
>> Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
>> ---
>>   tests/generic/371 | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tests/generic/371 b/tests/generic/371
>> index b312c450..95af308e 100755
>> --- a/tests/generic/371
>> +++ b/tests/generic/371
>> @@ -19,7 +19,7 @@ _require_scratch
>>   _require_xfs_io_command "falloc"
>>   test "$FSTYP" = "xfs" && _require_xfs_io_command "extsize"
>>   
>> -_scratch_mkfs_sized $((256 * 1024 * 1024)) >> $seqres.full 2>&1
>> +_scratch_mkfs_sized $((330 * 1024 * 1024)) >> $seqres.full 2>&1
>>   _scratch_mount
>>   
>>   # Disable speculative post-EOF preallocation on XFS, which can grow fast enough
>> -- 
>> 2.34.1
>>
-- 
Nirjhar Roy
Linux Kernel Developer
IBM, Bangalore