When adding a RawPageSpace and doing many acquire() and release() calls, I sometimes get a crash because the following line in FreeListPageResource.freeContiguousChunk() fails, i.e., returns -1: int tmp = freeList.alloc(Space.PAGES_IN_CHUNK, chunkStart); // then alloc the entire chunk Many Log.write()s later I think there may be a corner case in FreeListPageResource.releasePages() that needs slightly different handling. The attached patch eliminates the errors I was getting, but could an MMTk expert please check the change and verify that it's correct since I don't fully understand the code? thanks, Mike