Hi Sagi & Jason, Thanks for the comments, please see inline. On Wednesday, February 02/26/20, 2020 at 15:05:59 -0800, Sagi Grimberg wrote: > > >Current nvmet-rdma code allocates MR pool budget based on host's SQ > >size, assuming both host and target use the same "max_pages_per_mr" > >count. But if host's max_pages_per_mr is greater than target's, then > >target can run out of MRs while processing larger IO WRITEs. > > > >That is, say host's SQ size is 100, then the MR pool budget allocated > >currently at target will also be 100 MRs. But 100 IO WRITE Requests > >with 256 sg_count(IO size above 1MB) require 200 MRs when target's > >"max_pages_per_mr" is 128. > > 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. Traces on Target: #cat /sys/kernel/debug/tracing/trace_pipe|grep -v "status=0x0" kworker/8:1H-2461 [008] .... 25476.995437: nvmet_req_complete: nvmet1: disk=/dev/ram0, qid=1, cmdid=3, res=0xffff8b7f2ae534d0, status=0x6 kworker/8:1H-2461 [008] .... 25476.995467: nvmet_req_complete: nvmet1: disk=/dev/ram0, qid=1, cmdid=4, res=0xffff8b7f2ae53700, status=0x6 kworker/8:1H-2461 [008] .... 25476.995511: nvmet_req_complete: nvmet1: disk=/dev/ram0, qid=1, cmdid=1, res=0xffff8b7f2ae53980, status=0x6 > > >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).
