svn commit: r343030 - in head/sys: cam conf dev/md dev/nvme fs/fuse fs/nfsclient fs/smbfs kern sys ufs/ffs vm

[Gleb Smirnoff]

  Enji,

On Thu, Feb 14, 2019 at 05:12:21PM -0800, Enji Cooper wrote:
E> > On Wed, Feb 13, 2019 at 07:24:50PM -0600, Justin Hibbits wrote:
E> > J> This seems to break 32-bit platforms, or at least 32-bit book-e
E> > J> powerpc, which has a limited KVA space (~500MB).  It preallocates I've
E> > J> seen over 2500 pbufs, at 128kB each, eating up over 300MB KVA,
E> > J> leaving very little left for the rest of runtime.
E> > J> 
E> > J> I spent a couple hours earlier today debugging with Mark Johnston, and
E> > J> his consensus is that the vnode_pbuf_zone is too big on 32-bit
E> > J> platforms.  Unfortunately I know very little about this area, so can't
E> > J> provide much extra insight, but can readily reproduce the issues I see
E> > J> triggered by this change, so am willing to help where I can.
E> > 
E> > Ok, let's roll back to old default on 32-bit platforms and somewhat
E> > reduce the default on 64-bits.
E> > 
E> > Can you please confirm that the patch attached works for you?
E> 
E>     Quick question: why was the value reduced by a factor of 4 on 64-bit platforms?

Fair question. Replying to you and Bruce.

This pool of pbufs is used for sendfile(2) and default value of nswbuf / 2
wasn't enough for modern several Gbit/s speeds. At Netflix we run with
nswbuf * 8, since we run up to 100 Gbit/s of sendfile traffic.

Together with new pbuf allocator I bumped the value up to what we use.
Apparently that was overkill for 32-bit machines, so for them I fully
switched it back to old value. Nobody is expected to use these machine
as high performance web servers.

Also, I decided to reduce the default for 64-bit machines as well. Not
everybody runs 100 Gbit/s, but I'd like to see default FreeBSD (no
tunables in loader.conf) to be able to run 10 Gbit/s and more. So
I've chosen a middle ground between old value of nswbuf / 2 and the
value we use at Netflix.

P.S. Ideally, this needs to be autotuned. The problem is that now we need
to pre-allocate pbufs.

-- 
Gleb Smirnoff