* gnu/system/file-systems.scm (swap-space)[priority, discard?]: Add them. * guix/build/syscalls.scm (SWAP_FLAG_PREFER, SWAP_FLAG_PRIO_MASK, SWAP_FLAG_PRIO_SHIFT, SWAP_FLAG_DISCARD): Add them. * gnu/build/file-systems.scm (swap-space->flags-bit-mask): Add it. * gnu/services/base.scm (swap-service-type): Use it. Signed-off-by: Ludovic Courtès <ludo@gnu.org>