Petri Savolainen(psavol) replied on github web page:

@@ -212,6 +214,55 @@ void shmem_test_basic(void)
        CU_ASSERT(0 == odp_shm_free(shm));
+ * maximum size reservation
+ */
+static void shmem_test_max_reserve(void)
+       odp_shm_capability_t capa;
+       odp_shm_t shm;
+       uint64_t size, align;
+       uint8_t *data;
+       uint64_t i;
+       memset(&capa, 0, sizeof(odp_shm_capability_t));
+       CU_ASSERT_FATAL(odp_shm_capability(&capa) == 0);
+       CU_ASSERT(capa.max_blocks > 0);
+       size  = capa.max_size;
+       align = capa.max_align;
+       /* Assuming that system has at least MAX_MEMORY_USED bytes available */
+       if (capa.max_size == 0 || capa.max_size > MAX_MEMORY_USED)
+               size = MAX_MEMORY_USED;

Implementation may have a limitation of e.g. 4GB due to limit of using a 32 bit 
address space reservation, etc. It would be waste to reserve 4GB of system 
memory for every ODP instance, as  implementation could not guarantee 4GB 
otherwise, as other applications allocate memory as well. So, init  phase there 
could be 4.2GB available, but by the time ODP application starts calling 
shm_reserve() there would be less than 4GB left and some reserves would fail.

So, implementation may have large upper limit, which is not related to amount 
of available memory but e.g. due implementation of the address mapping (number 
of bits, hugepages, etc).

> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
> Same story as for `capa.max_size`. I'd expect most implementations to return 
> `capa.max_align` to be either 0 or some reasonable value like 4K or 1M. 
> However, if they specify something else then they should be able to deliver 
> that.

>> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
>> If the implementation doesn't have a specific predefined upper limit then it 
>> should return `capa.max_size == 0`. If it says it has a non-zero upper limit 
>> then if it's unable to provide that limit that's a failure. Otherwise what's 
>> the point of having a specified limit?

>>> Petri Savolainen(psavol) wrote:
>>> I'll add comment about zero value. Although, I already changed 
>>> documentation to require param_init() call and say that don't change values 
>>> that you are not going to use (init sets it to zero).

>>>> Petri Savolainen(psavol) wrote:
>>>> OK

>>>>> Petri Savolainen(psavol) wrote:
>>>>> Very large align could result very large allocation and thus again system 
>>>>> run out of memory (e.g. 1TB align => >1TB alloc).
>>>>> OK. I'll change align max to be a power of two. 

>>>>>> Petri Savolainen(psavol) wrote:
>>>>>> Since actual amount of available memory typically depends on system 
>>>>>> load. SHM implementation may not have a limit (max_size==0), or limit 
>>>>>> may be due to address space (e.g. 40bit == 1TB). System might not have 
>>>>>> always the max amount (e.g. 1TB) available. I limit validation test to 
>>>>>> assume that at least 100MB should be always available.

>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
>>>>>>> @muvarov `odp_shm_capability()` already tells the application the 
>>>>>>> largest contiguous size it can reserve (`max_size`) and the maximum 
>>>>>>> number of reserves it can do (`max_blocks`). This is just hinting to 
>>>>>>> the implementation the total size of all reserves the application will 
>>>>>>> do.

>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
>>>>>>>> An additional `printf()` giving a bit more detail (i.e., `i` value) 
>>>>>>>> would be useful here.

>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
>>>>>>>>> Shouldn't `MEGA` be a power of 2 for alignment purposes? I.e., 1024 x 
>>>>>>>>> 1024 rather than 1000 x 1000? And if the implementation supports an 
>>>>>>>>> even higher `max_align` why not test that as well?

>>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
>>>>>>>>>> Why do you want to limit the size in a test that named 
>>>>>>>>>> `shmem_test_max_reserve()`? If `capa.max_size == 0` then you have to 
>>>>>>>>>> pick a specific target, but if it's non-zero why wouldn't you want 
>>>>>>>>>> to try to reserve that much to see if the limit is true?

>>>>>>>>>>> muvarov wrote
>>>>>>>>>>> 0 - means not specified. And what about continuous of memory 
>>>>>>>>>>> chunks? Requesting  one big continues shared memory chunk is not 
>>>>>>>>>>> general solution.
updated_at 2018-02-02 13:49:37

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