The document discusses several key aspects of processes and memory management in Linux: 1. A process is represented by a task_struct structure that contains information like the process ID, open files, address space, and state. 2. Each process has both a user stack and kernel stack. The kernel stack is fixed size for safety and to prevent fragmentation. 3. Process duplication is done through fork(), vfork(), and clone() system calls. Fork uses copy-on-write to efficiently duplicate the process. 4. Memory allocation for kernel structures like task_struct uses slab allocators to improve performance over the buddy allocator through object caching and reuse.

1. 06/21/11 UPDATES Isa Ansharullah

6. 06/21/11 Process’ Kernel Stack (2) Professional Linux Kernel Architecture, Wolfgang Mauer p.71 task_struct is referenced via thread_info structure at the bottom of kernel stack (to provide fast access)

9. 06/21/11 FORKING PROCESS fork() clone() do_fork() defined in <kernel/fork.c> architecture-independent copy_process() The actual work of duplicating process Takes several flags about resources sharing, etc. If new child is returned successfully, The new child is woken up and run. In the common case, child will call exec() immediately, thus no overhead cost on copying. Thanks to Copy-on-write .

10. 06/21/11 <kernel/fork.c > copy_process() Creates a new kernel stack, task_struct, thread_info struct- tures similar to its parent’s Copy/Share resources Professional Linux Kernel Architecture, p73 Professional Linux Kernel Architecture, p68

16. 06/21/11 Not only task_struct ... ( from kernel/fork.c ) many structures are also allocated using the slab allocator

18. Overview 07/04/11 The memory is organized in caches , one cache for each object type. (e.g. inode_cache, dentry_cache, buffer_head, vm_area_struct) . Each cache consists out of many slabs (they are small (usually one page long) and always contiguous), and each slab contains multiple initialized objects. From linux/mm/slab.c header comment :

19. include/linux/slab_def.h | struct kmem_cache 07/04/11 struct kmem_cache { struct array_cache *array[NR_CPUS]; unsigned int batchcount; unsigned int limit; unsigned int shared; unsigned int buffer_size; u32 reciprocal_buffer_size; unsigned int flags; unsigned int num; unsigned int gfporder; gfp_t gfpflags; size_t colour; unsigned int colour_off; struct kmem_cache *slabp_cache; unsigned int slab_size; unsigned int dflags; void (*ctor) (void *obj); const char *name; struct list_head_next; struct kmem_list3 *nodelists[MAX_NUMNODES]; }

20. 06/21/11 /proc/slabinfo - seeing the caches from : isa’s personal VPS @ webbynode.com

22. 06/21/11 kernel/fork.c | dup_task_struct() ( continues.. )

28. cat /proc/buddyinfo order Showing available memory blocks in each zones 0 1 2 3 4 5 6 7 8 9 10

33. /bin/gonzo’s address space http://duartes.org/gustavo/blog/post/how-the-kernel-manages-your-memory

34. pmap <pid> Linux kernel Development, Robert Love p.314 library ELF library