Fwd: [PATCH] cifs: add .splice_write

[Andrés Souto]

I have been trying to reproduce it with a localhost samba and I wasn't able
to.
I also tried adding delays and limiting bandwidth using tc with the idea of
replicating network delays of a gigabit ethernet network but I didn't see a
significant difference either.

So I investigate what is the difference between writing to the NAS
(where I discovered the problem) compared to the samba at localhost and I
see
a completely different behaviour in the amount of data carried by each SMB
message.

writing to NAS
-----------------------------
read/write 64kB         64kB
read/write 1MB        1024kB
splice 64kB            4096B
splice 64kB (PATCH)     64kB
splice 1MB (PATCH)    1024kB


writing to localhost samba
---------------------------
read/write 64kB         1MB
splice 64kB             1MB
splice 64kB (PATCH)     1MB

In every case, the server seems to send one ack SMB message for each block
of data and
client doesn't sends new data until the ack is received. I suppose this
explains why
the throughput is ridiculous low for the situations when a SMB message
carries so little data.