On 10/27/07, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
I would like to understand more about your patches to see what bdi
values makes sense for CIFS and how to report possible congestion back
to the page manager. I had been thinking about setting bdi->ra_pages
so that we do more sensible readahead and writebehind - better
matching what is possible over the network and what the server
prefers. SMB/CIFS Servers typically allow a maximum of 50 requests
in parallel at one time from one client (although this is adjustable
for some). The CIFS client prefers to do writes 14 pages (an iovec of
56K) at a time (although many servers can efficiently handle multiple
of these 56K writes in parallel). With minor changes CIFS could
handle even larger writes (to just under 64K for Windows and just
under 128K for Samba - the current CIFS Unix Extensions allow servers
to negotiate much larger writes, but lacking a "receivepage"
equivalent Samba does not currently support larger than 128K).
Ideally, to improve large file copy utilization, I would like to see
from 3-10 writes of 56K (or larger in the future) in parallel. The
read path is harder since we only do 16K reads to Windows and Samba -
but we need to increase the number of these that are done in parallel
on the same inode. There is a large Google Summer of Code patch for
this which needs more review.
--
Thanks,
Steve
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