Messages in this thread | | | Subject | Re: Creating compressed backing_store as swapfile | From | "Austin S. Hemmelgarn" <> | Date | Mon, 5 Nov 2018 11:55:58 -0500 |
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On 11/5/2018 11:53 AM, valdis.kletnieks@vt.edu wrote: > 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... > Indeed, and I can't really comment on how it might behave under those circumstances (the systems I did the testing on never saw memory pressure quite _that_ bad, and I had them set up to swap things out pretty early and really aggressively).
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