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I noticed that a btrfs volume with compression enabled (e.g. 'compress=zstd') seems to compress inline data unconditionally, even in situations when compression is ineffective and only leads to increase in size. It is easily reproducible on small files: # echo 'a file with test content' > test.txt # sync # compsize test.txt Processed 1 file, 0 regular extents (0 refs), 1 inline. Type Perc Disk Usage Uncompressed Referenced TOTAL 172% 43B 25B 25B zstd 172% 43B 25B 25B Same file when no compression enabled: Processed 1 file, 0 regular extents (0 refs), 1 inline. Type Perc Disk Usage Uncompressed Referenced TOTAL 100% 25B 25B 25B none 100% 25B 25B 25B It's not a big deal on practice, but shouldn't it detect that the file is uncompressible and fall back to no compression? Also, if I remember correctly, it wasn't the case a couple of kernel releases back.