On 14-Mar-18 4:12 PM, Andrew Rybchenko wrote:
On 03/14/2018 05:40 PM, Burakov, Anatoly wrote:
On 10-Mar-18 3:39 PM, Andrew Rybchenko wrote:
The callback was introduced to let generic code to know octeontx
mempool driver requirements to use single physically contiguous
memory chunk to store all objects and align object address to
total object size. Now these requirements are met using a new
callbacks to calculate required memory chunk size and to populate
objects using provided memory chunk.
These capability flags are not used anywhere else.
Restricting capabilities to flags is not generic and likely to
be insufficient to describe mempool driver features. If required
in the future, API which returns structured information may be
added.
Signed-off-by: Andrew Rybchenko <arybche...@solarflare.com>
---
Just a general comment - it is not enough to describe minimum memchunk
requirements. With memory hotplug patchset that's hopefully getting
merged in 18.05, memzones will no longer be guaranteed to be
IOVA-contiguous. So, if a driver requires its mempool to not only be
populated from a single memzone, but a single *physically contiguous*
memzone, going by only callbacks will not do, because whether or not
something should be a single memzone says nothing about whether this
memzone has to also be IOVA-contiguous.
So i believe this needs to stay in one form or another.
(also it would be nice to have a flag that a user could pass to
mempool_create that would force memzone reservation be
IOVA-contiguous, but that's a topic for another conversation. prime
user for this would be KNI.)
I think that min_chunk_size should be treated as IOVA-contiguous.
Why? It's perfectly reasonable to e.g. implement a software mempool
driver that would perform some optimizations due to all objects being in
the same VA-contiguous memzone, yet not be dependent on underlying
physical memory layout. These are two separate concerns IMO.
> So, we
have 4 levels:
- MEMPOOL_F_NO_PHYS_CONTIG (min_chunk_size == 0) -- IOVA-congtiguous
is not required at all
- no MEMPOOL_F_NO_PHYS_CONTIG (min_chunk_size == total_obj_size) --
object should be IOVA-contiguous
- min_chunk_size > total_obj_size -- group of objects should be
IOVA-contiguous
- min_chunk_size == <all-objects-size> -- all objects should be
IOVA-contiguous
I don't think this "automagic" decision on what should be
IOVA-contiguous or not is the way to go. It needlessly complicates
things, when all it takes is another flag passed to mempool allocator
somewhere.
I'm not sure what is the best solution here. Perhaps another option
would be to let mempool drivers allocate their memory as well? I.e.
leave current behavior as default, as it's likely that it would be
suitable for nearly all use cases, but provide another option to
override memory allocation completely, so that e.g. octeontx could just
do a memzone_reserve_contig() without regard for default allocation
settings. I think this could be the cleanest solution.
If so, how allocation should be implemented?
1. if (min_chunk_size > min_page_size)
a. try all contiguous
b. if cannot, do by mem_chunk_size contiguous
2. else allocate non-contiguous
--
Andrew.
--
Thanks,
Anatoly
