nfs client and io_uring zero copy receive

[Anton Gavriliuk <antosha20xx@xxxxxxxxx>]

Hi

I am trying to exceed 20 GB/s doing sequential read from a single file
on the nfs client.

perf top shows excessive memcpy usage:

Samples: 237K of event 'cycles:P', 4000 Hz, Event count (approx.):
120872739112 lost: 0/0 drop: 0/0
Overhead  Shared Object                      Symbol
  20,54%  [kernel]                           [k] memcpy
   6,52%  [nfs]                              [k] nfs_generic_pg_test
   5,12%  [nfs]                              [k] nfs_page_group_lock
   4,92%  [kernel]                           [k] _copy_to_iter
   4,79%  [kernel]                           [k] gro_list_prepare
   2,77%  [nfs]                              [k] nfs_clear_request
   2,10%  [nfs]                              [k] __nfs_pageio_add_request
   2,07%  [kernel]                           [k] check_heap_object
   2,00%  [kernel]                           [k] __slab_free

Can nfs client be adopted to use zero copy ?, for example by using
io_uring zero copy rx.

Anton