Re: posix_fallocate behavior in glibc

[Christoph Hellwig <hch@lst.de>]

Hi Paul,

thanks for the answer.  I don't have a current glibc assignment, so me
directly sending a patch is probably not productive.

I don't really know which file systems benefit from doing a zeroing
operations - after all this requires writing the data twice which usually
actually is a bad idea unless offset by extremely suboptimal allocation
behavior for small allocations, which got fixed in most file systems
people actually use.  So candidates where it actually would be useful
might be things like hfsplus.  But these are often used on cheap
consumer media, where the double write will actually meaningfully cause
additional write and erase cycle harming the device lifetime and long
term performance.

Note that the kernel has a few implementations of fallocate that are
basically a slightly more optimized implementation of this pattern
(fat, gfs2) so some maintainers through it useful at least for
some workloads and use cases.