Message-ID: <052801db937c$9bbf12a0$d33d37e0$@thebergstens.com>
Date: Wed, 12 Mar 2025 11:28:50 -0700
From: "James R. Bergsten" <jim@...bergstens.com>
To: "'Christoph Hellwig'" <hch@...radead.org>,
	"'Matthew Wilcox'" <willy@...radead.org>
Cc: "'Hannes Reinecke'" <hare@...e.de>,
	"'Vlastimil Babka'" <vbabka@...e.cz>,
	"'Hannes Reinecke'" <hare@...e.com>,
	"'Boris Pismenny'" <borisp@...dia.com>,
	"'John Fastabend'" <john.fastabend@...il.com>,
	"'Jakub Kicinski'" <kuba@...nel.org>,
	"'Sagi Grimberg'" <sagi@...mberg.me>,
	<linux-nvme@...ts.infradead.org>,
	<linux-block@...r.kernel.org>,
	<linux-mm@...ck.org>,
	"'Harry Yoo'" <harry.yoo@...cle.com>,
	<netdev@...r.kernel.org>
Subject: RE: Networking people smell funny and make poor life choices

OK another "unnecessary" old-timer storage/network story/disruption to your otherwise relevant discussions (thank the subject line). If you're too busy, just don't read it. 😊

Around 1985, Gene Amdahl founded a company called Andor. Its original purpose (as was with everything Gene did) was to build the smallest plug-compatible mainframe.  When it was designed, someone noted it had no physical room for the humongous "Bus and Tag" cables needed for peripherals, so Gene raised a bit more money and started a storage project too.

When the Loma Prieta earthquake happened in 1989, PG&E, the local utility, lost the datacenter containing all of the information needed to repair their utilities, so the service people had to do this from memory.  The Public Utilities Commission didn't find this terribly funny, so they said PG&E had to create a second datacenter out of the area immediately and have backups there within about 24 hours, shorter as time went on.  So, they shut down the primary site every night, dumped to tape, then drove it up to Sacramento where these were restored.  They named this CTAM for "Chevy Truck Access Method."

Somehow Gene and friends heard about this and, as they already had a processor, device simulation and devices, if they added some sort of networking interface, they could have a local unit and a remote unit doing this backup, eliminating the truck.  BTW the "front end" storage group all came from Memorex.  The "back end" group mostly from Amdahl.

This actually (somewhat) worked, and a couple of units were installed in beta sites.  Sadly, Gene ran out of money (or at least didn't accept the terms offered) and buggered off to start yet another mainframe company which never shipped anything.

I was the last Engineering VP at Andor, so when it folded, I grabbed a few of the people and started a similar company but for the open systems market instead.  We named it "Ark" at my wife's suggestion as was like Noah's Ark - "disaster recovery" and "two of everything."  We mostly bootstrapped, did ship product, and were acquired by LSI Logic who were getting beaten around the head as EMC had a remote solution, but LSI didn't. I got about a dozen US Patents Issued and enough money to finally buy a house in Silicon Valley.

Our (SCSI-based) device had front end ports for the host(s), back-end ones for the devices, and side ones for the networking.  Lots of features, some you folks are only doing recently.  Looked like devices to hosts, hosts to devices.

Anyway, the point of all of this is that when we sold it to customers, the storage people looked at the network ports with confusion and dismay (some hadn't even ordered the network lines and caused months of delay), while the network people looked at the device ports as if they were full of Tasmanian devils.

Turned out, both network and storage expertise were very rare commodities.  This was largely why most iSCSI startups failed, they either did a storage product or a networking product. We pilled this off because I am stupid but stubborn and wrote the RTOS myself (Linux was in its infancy and the other RTOS's sucked).  Seemed a good idea at the time.  Have white papers online if anybody is interested.

So, networking people may smell funny, but to them storage people come from another galaxy.  Working in this industry at all could be considered a poor life choice but that's for another time.

Sorry. You can go back to work now.
Jim B

-----Original Message-----
From: Linux-nvme <linux-nvme-bounces@...ts.infradead.org> On Behalf Of Christoph Hellwig
Sent: Wednesday, March 12, 2025 8:09 AM
To: Matthew Wilcox <willy@...radead.org>
Cc: Hannes Reinecke <hare@...e.de>; Vlastimil Babka <vbabka@...e.cz>; Hannes Reinecke <hare@...e.com>; Boris Pismenny <borisp@...dia.com>; John Fastabend <john.fastabend@...il.com>; Jakub Kicinski <kuba@...nel.org>; Sagi Grimberg <sagi@...mberg.me>; linux-nvme@...ts.infradead.org; linux-block@...r.kernel.org; linux-mm@...ck.org; Harry Yoo <harry.yoo@...cle.com>; netdev@...r.kernel.org
Subject: Re: Networking people smell funny and make poor life choices

On Wed, Mar 05, 2025 at 06:11:24PM +0000, Matthew Wilcox wrote:
> Networking needs to follow block's lead and STOP GETTING REFCOUNTS ON 
> PAGES.

The block layer never took references on pages.  The direct I/O helpers that just happened to set in block/ did hold references and abused some field in the bio for it (and still do for the pinning), but the reference was (and the pin now is) owned by the submitter.

The block layer model has always been that the submitter needs to ensure memory stays allocated until the I/O has completed.  Which IMHO is the only sane model for dealing with memory lifetimes vs I/O, and something networking absolutely should follow.

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