Re: network outages

At Sat, 21 Mar 2026 16:54:36 -0000 (UTC), [email protected] (Michael van Elst) wrote:
Subject: Re: network outages
>
> 262144 * 2048 / ( 512 + 2048 ) = 209715.
>
> The relevant setting is kern.sbmax. Setting a socket buffer beyond
> sbmax * MCLBYTES / (MSIZE + MCLBYTES) fails and the TCP protocol
> no longer attaches.
>
> The correction factor obviously should make kern.sbmax show the
> total memory used for a buffer including the headers.  But it's
> just confusing.

Isn't the simplest to just make kern.sbmax the right size for the
largest given {send,recv}buf_max value?

I.e.:

	kern.sbmax = buf_max + ((buf_max / MCLBYTES) * MSIZE)

No?

Could the kernel do this itself and eliminate the need to manually tune
kern.sbmax?  Maybe even eliminate kern.sbmax entirely?

So, folks using 16Mb for sendbuf_max need to set kern.sbmax to 20Mb, no?

--
					Greg A. Woods <[email protected]>

Kelowna, BC     +1 250 762-7675           RoboHack <[email protected]>
Planix, Inc. <[email protected]>     Avoncote Farms <[email protected]>

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