Petri Savolainen(psavol) replied on github web page:
platform/linux-generic/_ishm.c
line 23
@@ -1436,15 +1436,23 @@ int _odp_ishm_cleanup_files(const char *dirpath)
return 0;
}
-int _odp_ishm_init_global(void)
+int _odp_ishm_init_global(const odp_init_t *init)
{
void *addr;
void *spce_addr;
int i;
uid_t uid;
char *hp_dir = odp_global_data.hugepage_info.default_huge_page_dir;
uint64_t align;
+ uint64_t max_memory = ODP_CONFIG_ISHM_VA_PREALLOC_SZ;
+ uint64_t internal = ODP_CONFIG_ISHM_VA_PREALLOC_SZ / 8;
Comment:
if (init && init->shm.max_memory)
max_memory = init->shm.max_memory + internal;
line 1455 does not underflow even with application requested
init->shm.max_memory value:
shm_max_size = init->shm.max_memory + internal - internal;
> muvarov wrote
> 'internal' has to be also adjusted. Or you can get overflow at line 1455.
>> Petri Savolainen(psavol) wrote:
>> If max size is 4GB, max align is 1GB. A resevation may consume e.g. 4.5GB
>> memory. Again it depends on other applications and ODP instances if such
>> amount of system memory is still free when application tries to reserve it.
>> Maybe first couple instances succeeded, but then system did run out of
>> memory.
>>> Petri Savolainen(psavol) wrote:
>>> In the example, system is 64 bit, has e.g. 32 GB of memory, ODP SHM
>>> implementation is limited e.g. by address space pre-reservation etc (e.g.
>>> 32 bits / 4GB). So, ODP implementation limits max SHM size to 4GB, 0 cannot
>>> be used as capability. A 4 GB reservation succeeds as long as system has
>>> memory free. When other applications or ODP instances have reserved all
>>> 32GB memory, yet another 4GB reservation will fail.
>>>
>>> So, 0 says that there's no other limit than amount of currently free
>>> memory. E.g. odp-linux implementation lied by returning 0 and at the same
>>> time limiting max reservation to 512MB (due to fixed size address space
>>> allocation).
>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
>>>> Again, what does the application gain from having a non-zero `max_align`
>>>> returned if it's unable to make use of it?
>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote:
>>>>> 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_r166543916
updated_at 2018-02-07 08:17:52
