Disclosed herein are system, method, and computer program product embodiments for defragmentation of persistent main memory (e.g., storage class memory). An embodiment operates by determining that a request to allocate a block of persistent main memory cannot be fulfilled, identifying the largest block of a plurality of free blocks associated with a persistent allocator, and punching a hole at the location of the block within a segment of the persistent main memory. The embodiment further operates by determining that at least one neighboring block of the largest block is also a hole, and coalescing the at least one neighboring block and the largest block.