• David Howells's avatar
    rxrpc: Preallocate peers, conns and calls for incoming service requests · 00e90712
    David Howells authored
    Make it possible for the data_ready handler called from the UDP transport
    socket to completely instantiate an rxrpc_call structure and make it
    immediately live by preallocating all the memory it might need.  The idea
    is to cut out the background thread usage as much as possible.
    
    [Note that the preallocated structs are not actually used in this patch -
     that will be done in a future patch.]
    
    If insufficient resources are available in the preallocation buffers, it
    will be possible to discard the DATA packet in the data_ready handler or
    schedule a BUSY packet without the need to schedule an attempt at
    allocation in a background thread.
    
    To this end:
    
     (1) Preallocate rxrpc_peer, rxrpc_connection and rxrpc_call structs to a
         maximum number each of the listen backlog size.  The backlog size is
         limited to a maxmimum of 32.  Only this many of each can be in the
         preallocation buffer.
    
     (2) For userspace sockets, the preallocation is charged initially by
         listen() and will be recharged by accepting or rejecting pending
         new incoming calls.
    
     (3) For kernel services {,re,dis}charging of the preallocation buffers is
         handled manually.  Two notifier callbacks have to be provided before
         kernel_listen() is invoked:
    
         (a) An indication that a new call has been instantiated.  This can be
         	 used to trigger background recharging.
    
         (b) An indication that a call is being discarded.  This is used when
         	 the socket is being released.
    
         A function, rxrpc_kernel_charge_accept() is called by the kernel
         service to preallocate a single call.  It should be passed the user ID
         to be used for that call and a callback to associate the rxrpc call
         with the kernel service's side of the ID.
    
     (4) Discard the preallocation when the socket is closed.
    
     (5) Temporarily bump the refcount on the call allocated in
         rxrpc_incoming_call() so that rxrpc_release_call() can ditch the
         preallocation ref on service calls unconditionally.  This will no
         longer be necessary once the preallocation is used.
    
    Note that this does not yet control the number of active service calls on a
    client - that will come in a later patch.
    
    A future development would be to provide a setsockopt() call that allows a
    userspace server to manually charge the preallocation buffer.  This would
    allow user call IDs to be provided in advance and the awkward manual accept
    stage to be bypassed.
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    00e90712
proc.c 5.41 KB