On Mon, 05 Nov 2018 11:28:49 -0500, "Austin S. Hemmelgarn" said: > Also, it's probably worth noting that BTRFS doesn't need to decompress > the entire file to read or write blocks in the middle, it splits the > file into 128k blocks and compresses each of those independent of the > others, so it can just decompress the 128k block that holds the actual > block that's needed.
Presumably it does something sane with block allocation for the now-compressed 128K that's presumably much smaller. Also, that limits the damage from writing to the middle of a compression unit.... That *does* however increase the memory requirement - you can OOM or deadlock if your read/write from the swap needs an additional 128K for the compression buffer at an inconvenient time...
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