Use fragment size for autoGC capacity calculation #3562
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Our Darwin builders at work weren't running auto-GC despite being configured to, so I had to step in here and figure out what's going on.
Turns out that in
struct statvfs,f_bsizeandf_frsizeare basically always the same on Linux, while on macOS,f_bsizemeasures a completely different statistic (optimal I/O read size), see the man page here.On my relatively new MBP running Catalina on APFS,
f_bsizeis 1MB whilef_frsizeis 4KB (the actual block size). Since we usef_bsizein the size calculation requirement, the capacity checks Nix does on Darwin are off by a factor of 256, and since we hadmax-freeconfigured, the machine was always considered to have ample space.The
gc-auto.shtest can't catch this since it stubs the reported FS capacity, and also I don't think there's any reasonable way for us to catch this in a test.I don't think there should be anything wrong with using
f_frsizefor both platforms since the two fields seem to always be the same on Linux, see StackOverflow.