[Bloat] using tcp_notsent_lowat in various apps?

[Dave Taht]

On Tue, Jun 16, 2015 at 9:33 AM, Jonathan Morton <chromatix99 at gmail.com> wrote:
>
>> On 16 Jun, 2015, at 19:18, Steinar H. Gunderson <sgunderson at bigfoot.com> wrote:
>>
>> On Tue, Jun 16, 2015 at 09:11:08AM -0700, Dave Taht wrote:
>>> I just tossed off a quick patch for rsync, not that I have a clue as
>>> to whether it would make any difference there.
>>
>> For bulk applications (like rsync), how would this make sense at all?
>> I thought the entire point of this option was if you knew what data to send
>> now, but that you might want to change your mind later if it takes some time
>> to send it. The latter doesn't apply to rsync.
>
> Actually, it does.  Rsync is designed to be used to update an existing set of files, so the protocol interleaves control and data information asynchronously.
>
> More generally, I think it’s worth setting LOWAT on *any* application that uses select() or poll() with a readable and writable socket population simultaneously.

Take samba as another potential example. I commonly see this
increasing the SO_SNDBUF to a given value, but I am not sure if this
is the right thing anymore. As samba is commonly used for filesharing
(and things that take locks and do database-y stuff), improving
interactivity might be a big win.

Seeing the 50%! decrease in kernel memory on the original tests of
TCP_SENT_LOWAT is very exciting in the context of those running samba
on tiny tiny nas devices common in my world.

And seeing apple enable it universally points to perhaps exploring the
effects of just enabling it universally in linux (or in certain kinds
of linux-based devices) at a "reasonable" value, for whatever value of
reasonable exists.

> - Jonathan Morton
>
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-- 
Dave Täht
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