Matthew Dillon wrote: > The nominal limit for swap space is around 14 GB due to limitations > in available KVM. There are three major limiting factors in the kernel: > > * The swap bitmap eats 2 bits per page of swap. The bitmap is sized > to handle NSWAP (default 4) x size_of_largest_swap_partition.
Is NSWAP tied to the NSWAPDEV kernel option, or is it the actual number of active swap devices? If the prior, is setting NSWAPDEV to the actual number of swap devices a useful for improving memory usage? Is NSWAPDEV just a compile-time tunable, or is there a sysctl to do the same thing? > * The system has to keep track of pages that are swapped out. > The system reserves 8 x <physical_pages_in_system> worth of > KVM to keep track of swapped out pages. A machine with 4G > of ram reserves enough KVA to hold 32GB worth of swapped out pages. > > * The system limits the size of the above zone to VM_SWZONE_SIZE_MAX, > which is typically around 70 MB of KVM (enough to hold 14 GB worth > of swap mappings). > > So the nominal limit is around 14 GB on a 32 bit architecture. With > tuning this limit can be bumped up, but the practical limit is > going to be around 60GB unless you give the kernel more KVA (reducing > the amount of VM a user process can access). Can VM_SWZONE_SIZE_MAX be tuned down as well, or does the kernel already handle this efficiently enough to keep it at a minimum useful value sized relative to PHYS? To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
