Xenomai Version : 2.2-rc2
Skin : native
Kernel : 2.4.25
Arch.: PPC
I try to test my Xenomai system with low memory.
As Linux kills processes which try to allocate more memory than available
(instead of returning just a NULL-pointer !??), I had to use the Xenomai heap
services to allocate (nearly) all available memory.
So first I create heaps of about 16MB (why are heaps limited ?) and then
allocate all the memory of the heap. Roughly like this (not perfect, I know) :
#define MEMORYCHUNKSIZE 16000000
addsize=memsize=MEMORYCHUNKSIZE; /*max Heapsize 16MB*/
s.memoryallocated=0;
for(i=0;i<20;i++)
{
sprintf(nbuf,"bigheap%d",i);
if(rt_heap_create(&bigheap[i],nbuf,memsize,H_PRIO|H_MAPPABLE))
break;
printf("heap %d of size %ld created\n",i,memsize);
if((ret=rt_heap_alloc(&bigheap[i],memsize,TM_NONBLOCK,&bigbuf[i])))
{
printf("Failed to allocate heap %d of size %ld
(Ret:%d)\n",i,memsize,ret);
bigbuf[i]=NULL;
bigsize[i]=0;
}
else
{
s.memoryallocated+=memsize;
printf("Heap %d allocated size %ld\n",i,memsize);
bigsize[i]=memsize;
}
}
First thing I noticed is, that more bytes are used than the size of heap :
/proc/xenomai/registry/native/heaps # more bigheap5
type=mappable:size=16000000:used=16003072
But this is probably all right (some administrative information I guess) ?
The method described above leaves some spare memory, the size of which I try to
determine by creating heaps of increasing size (heaps are destroyed as soon as
they are succesfully created).
After knowing the size of the spare memory, I create a heap a little bit
smaller (e.g. half the spare size), which is successful.
Buuut, when allocating this memory (rt_heap_alloc) I get the error -EAGAIN
(-11; unfortunately not documented). As EAGAIN suggest I tried to allocate
memory again and again, but it never is successful.
So, can some friendly guru explain to me :
- why rt_heap_alloc fails
- what the error -EAGAIN means
- why heaps are limited to 16MB
- is there a function telling me how much memory is available (to avoid linux
tasks beeing killed).
Again I have to thank you in advance for the time you invest for the comunity
(I don´t know what I would do without your advice)
Roderik
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