A rationale is given in the comments, but even a class 6 or class 10 SD card can handle reads and writes on the order of MB/s, which means a 4KB chunk size is just wasting time in syscalls. This could maybe be fixed with a buffering reader but I don't feel comfortable tweaking libretro-common's VFS to handle that. Instead, I thought it would be good to both remove an ifdef and increase the chunk size to 128KB. For cores with small states this will should make state saving virtually instantaneous, and for cores with large states it should be a 32x speedup.
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