Re: stable page writes: wait_on_page_writeback and packet signing

[Jeff Layton <jlayton@redhat.com>]

On Wed, 9 Mar 2011 16:01:30 -0600
Steve French <smfrench@gmail.com> wrote:

> 
> Except we don't need to wait that long with the page locked
> ie for a response from the cifs server (such as Samba or Windows
> or NetApp), just need to wait for it to get on the wire.
> Waiting for us to get the server response would
> take 10 or 100 times longer.   In any case we can't resend
> the same request to the server (the signature changes on the
> resend since the sequence number is incremented on every
> request/response so we have to recalc the checksum anyway) and
> cifs requests can't get lost (as with nfs over udp).  Keeping
> a page locked for 10milliseconds seems like a bad idea - but
> it is a little more complicated to implement (for the cifs case)
> so that we end page writeback (for the non-WB_SYNC)
> as quickly as reasonably possible so we don't kill perf.
> 

The problem here is that the socket layer doesn't have a mechanism
to notify us of a TCP ACK. So, we have to wait for the next-best thing
-- a response from the server.

-- 
Jeff Layton <jlayton@redhat.com>