Re: [dpdk-dev] [PATCH 0/4] Allow using external memory without malloc

[Shahaf Shuler <shahafs@mellanox.com>]

Hi Anatoly, 

Thursday, November 29, 2018 3:49 PM, Anatoly Burakov:
> Subject: [PATCH 0/4] Allow using external memory without malloc
> 
> Currently, the only way to use externally allocated memory is through
> rte_malloc API's. While this is fine for a lot of use cases, it may not be suitable
> for certain other use cases like manual memory management, etc.
> 
> This patchset adds another API to register memory segments with DPDK (so
> that API's like ``rte_mem_virt2memseg`` could be relied on by PMD's and
> such), but not create a malloc heap out of them.
> 
> Aside from the obvious (not adding memory to a heap), the other major
> difference between this API and the ``rte_malloc_heap_*`` external memory
> functions is the fact that no DMA mapping is performed automatically.
> 
> This really draws a line in the sand, and there are now two ways of doing
> things - do everything automatically (using the ``rte_malloc_heap_*`` API's),
> or do everything manually (``rte_extmem_*`` and future DMA mapping API
> [1] that would replace ``rte_vfio_dma_map``). This way, the consistency of
> API is kept, and flexibility is also allowed.
> 

As you know I like the idea.
One question though, do you see a use case for application to have externally allocated memory which needs to be registered to the DPDK subsystem however not being used for DMA?
My only guess would be so helper libraries which requires the memory allocation from user (however it doesn't seems like a good API). 

If no use case, maybe it is better to merge between the two (rte_extmem_* and rte_dma_map) to have a single call for app to register and DMA map the memory. The rte_mem_virt2memseg is not something application needs to understand, it is used internally by PMDs or other libs. 

> [1]
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fma
> ils.dpdk.org%2Farchives%2Fdev%2F2018-
> November%2F118175.html&data=02%7C01%7Cshahafs%40mellanox.co
> m%7C007a9234feaf42c82f6508d656015eb1%7Ca652971c7d2e4d9ba6a4d1492
> 56f461b%7C0%7C0%7C636790961244424277&sdata=YqwcPEEhJM3I7Toe
> Ne%2BGcbeo%2FmPbYEnNFckoA7ES2Hg%3D&reserved=0
> 
> Note: at the time of this writing, there's no release notes
>       template, so no release notes updates in this patchset.
>       They will be added in later revisions.
> 
> Anatoly Burakov (4):
>   malloc: separate creating memseg list and malloc heap
>   malloc: separate destroying memseg list and heap data
>   mem: allow registering external memory areas
>   mem: allow usage of non-heap external memory in multiprocess
> 
>  .../prog_guide/env_abstraction_layer.rst      |  63 +++++++--
>  lib/librte_eal/common/eal_common_memory.c     | 116
> +++++++++++++++++
>  lib/librte_eal/common/include/rte_memory.h    | 122
> ++++++++++++++++++
>  lib/librte_eal/common/malloc_heap.c           | 104 +++++++++++----
>  lib/librte_eal/common/malloc_heap.h           |  15 ++-
>  lib/librte_eal/common/rte_malloc.c            | 115 +++++++----------
>  lib/librte_eal/rte_eal_version.map            |   4 +
>  7 files changed, 434 insertions(+), 105 deletions(-)
> 
> --
> 2.17.1