readme.allocator

fsmlabs的real time linux的内核

rtl_malloc(size) to allocate dynamik memory from a rt_thread.

concept of operation:

 rtl_alloc will eventually call kmalloc with GFP_ATOMIC - to do this without
 blocking execution of rt-threads (even if its a high priority thread that 
 requests memory) a tasklet that runs in linux kernel space is set up to 
 actually do the allocation. 

 a global pointer array for memory pointers is statically initiated in the
 module (private to the module for now).
 
 init module assignes NULL pointers to the entire array of pointers 

 RT-Thread calls rtl_alloc passing it the size requsted
 rtl_alloc will call the tasklet and suspend the rt-thread.
 allocator_tasklet kmallocs the memory zerrors it and then signals 
 RTL_SIGNAL_WACKUP to the suspended thread.
 The RT-thread needs to check the return value of rtl_alloc to know if the 
 memory allocation was successfull.

 cleanup module frees the memory by calling kfree on each non-NULL pointer

The implementation is only a prof of concept - the allocation strategy itselfe
is unusable as there is no free/reuse of buffers posible and memory is blocked
until rmmod is called. The allocation strategy though is up to the allocator
tasklet as it is only getting the size and returning the index into the memory
pointer list - so optimization and reuse can be put into the allocator tasklet.

The rt_allocator.o module will now simply start a rt-thread and allocate
increasing blocks of memory until the pointers are exhausted then loop on
for ever failing on rtl_malloc , on rmmod the thread is terminated and 
memory is freed.

Note that kmalloc is limited to 128KB - if your request more you will get a 
pointer to a 128K block - no warning.