Re: [PATCH for-rc] nvme-rdma/nvmet-rdma: Allocate sufficient RW ctxs to match hosts pgs len

[Sagi Grimberg <sagi@grimberg.me>]

>> The patch doesn't say if this is an actual bug you are seeing or
>> theoretical.
> 	
> I've noticed this issue while running the below fio command:
> fio --rw=randwrite --name=random --norandommap --ioengine=libaio
> --size=16m --group_reporting --exitall --fsync_on_close=1 --invalidate=1
> --direct=1 --filename=/dev/nvme2n1 --iodepth=32 --numjobs=16
> --unit_base=1 --bs=4m --kb_base=1000
> 
> Note: here NVMe Host is on SIW & Target is on iw_cxgb4 and the
> max_pages_per_mr supported by SIW and iw_cxgb4 are 255 and 128
> respectively.

This needs to be documented in the change log.

>>> The proposed patch enables host to advertise the max_fr_pages(via
>>> nvme_rdma_cm_req) such that target can allocate that many number of
>>> RW ctxs(if host's max_fr_pages is higher than target's).
>>
>> As mentioned by Jason, this s a non-compatible change, if you want to
>> introduce this you need to go through the standard and update the
>> cm private_data layout (would mean that the fmt needs to increment as
>> well to be backward compatible).
> 
> Sure, will initiate a discussion at NVMe TWG about CM private_data format.
> Will update the response soon.
>>
>>
>> As a stop-gap, nvmet needs to limit the controller mdts to how much
>> it can allocate based on the HCA capabilities
>> (max_fast_reg_page_list_len).

Sounds good, please look at capping mdts in the mean time.