A method for storing data in a memory that includes multiple memory blocks, includes running a compaction process that selects one or more memory blocks containing both valid data and invalid data, copies the valid data from the selected memory blocks to other storage locations, and then erases the selected memory blocks. At least one memory block, which meets a criterion predictive of imminent invalidation of at least some of the data in the block, is identified. Selection of the identified memory block in the compaction process is inhibited.