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The vm.swappiness sysctl controls the kernel's prefernce for swapping anonymous memory vs page cache. Since Scylla uses very large amounts of anonymous memory, and tiny amounts of page cache, the correct setting is to prefer swapping page cache. If the kernel swaps anonymous memory the reactor will stall until the page fault is satisfied. On the other hand, page cache pages usually belong to other applications, usually backup processes that read Scylla files. This setting has been used in production in Scylla Cloud for a while with good results. Users can opt out by not installing the scylla-kernel-conf package (same as with the other kernel tunables).