Bill Fischofer(Bill-Fischofer-Linaro) 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;

The 0 value is intended to say that addressability / available memory is the 
only limit, so again in this case the implementation should return 0, not 4GB. 
If the implementation says 0 and the application tries to reserve something 
huge and that fails that's OK. The application needs to check RCs in any event. 
But what's the point of having a non-zero limit if there's no reasonable 
expectation that it means anything? At that point it's useless and might as 
well be ignored.

> Petri Savolainen(psavol) wrote:
> Maybe with 1GB hugepages the max align is 1GB, and 16GB hugepages 16GB, ...

>> Petri Savolainen(psavol) wrote:
>> 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 14:38:58

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