Bill Fischofer(Bill-Fischofer-Linaro) replied on github web page:
test/validation/api/shmem/shmem.c
@@ -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;
Comment:
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.
https://github.com/Linaro/odp/pull/446#discussion_r165661012
updated_at 2018-02-02 14:38:58
