Preparing for nonvolatile RAM

Posted May 29, 2012 20:40 UTC (Tue) by daglwn (guest, #65432)
In reply to: Preparing for nonvolatile RAM by viro
Parent article: Preparing for nonvolatile RAM

Come on Al, you're being deliberately dense. All that filesystem code ALSO optimizes access for rotating storage, does buffering, etc. Why the heck do we need a file cache at all if we don't have a slow disk?

There is a lot of complex code that could be dumped if everything lived in a random-access memory. Device drivers alone would be a huge savings.

Preparing for nonvolatile RAM

Posted May 29, 2012 21:33 UTC (Tue) by paulj (subscriber, #341) [Link] (5 responses)

I'm curious, where in the VFS is the complex code for optimising rotating storage, buffering, etc? Or where/how does the API for the VFS require fs implementations to do that kind of thing?

Preparing for nonvolatile RAM

Posted May 30, 2012 1:36 UTC (Wed) by daglwn (guest, #65432) [Link] (4 responses)

If you don't have a filesystem model you don't have a VFS and you don't have filesystems. I'm really quite surprised at the pushback here. It's an idea. Don't get bent out of shape.

Preparing for nonvolatile RAM

Posted May 30, 2012 4:43 UTC (Wed) by dlang (guest, #313) [Link] (1 responses)

There are a lot of people who have advocated eliminating filesystems.

However, they have always run into the stumbling block that it's just impractical to deal with all hunks of data in a flat namespace. Directories are EVIL, but nobody has make anything else work even one tenth as well

Also, just keeping everything in ram falls apart as soon as you want someone else to access it (or you loose the device, or the device gets destroyed, or ...)

Many of the people pushing back have been though this "eliminate filesystems" experiment before and have the scars to show for it. Listen and learn (then go try and build something to prove them wrong :-)

Preparing for nonvolatile RAM

Posted May 31, 2012 19:35 UTC (Thu) by timka.org (guest, #53366) [Link]

Dmitry Zavalishin, the author of Phantom OS (which "eliminates filesystems"), was asked the question about removable storage when he was giving a talk about the OS at HighLoad++ in 2009.

His idea is to start a separate Phantom VM for a removable media which then can be seen as another "host" accessible via "network". AFAIU, this means Phantom's native IPC is substituted by some protocol. Smells somewhat like Plan 9 to me.

Preparing for nonvolatile RAM

Posted May 30, 2012 4:52 UTC (Wed) by paulj (subscriber, #341) [Link] (1 responses)

But you said you would still have a layer to provide user-friendly namespace, and a translation between that and the actual memory handles. You seem to think the current VFS is far more than that, that the current VFS does things like block-IO buffering and has other arcane IO related knowledge. So where does the VFS have anything like that?

Preparing for nonvolatile RAM

Posted May 30, 2012 14:54 UTC (Wed) by daglwn (guest, #65432) [Link]

The VFS doesn't. The fs layers and drivers do.

I think the discussion is pretty pointless now...

Preparing for nonvolatile RAM

Posted May 30, 2012 0:11 UTC (Wed) by Trelane (subscriber, #56877) [Link] (1 responses)

> Why the heck do we need a file cache at all if we don't have a slow disk?

Because not all memory is the same, let alone the pipe over which we get it.

How would you use a hypothetical storage medium that had 1EB of storage but you could only access it at 128kbps?

Preparing for nonvolatile RAM

Posted May 30, 2012 1:37 UTC (Wed) by daglwn (guest, #65432) [Link]

Probably the same way we handle networks today.

The filesystem is the abstraction and that abstraction has certain costs. Changing the abstraction doesn't imply we immediately forget everything we know.

Preparing for nonvolatile RAM

Posted May 30, 2012 6:53 UTC (Wed) by viro (subscriber, #7872) [Link] (4 responses)

RTFS. I've even told you which source to read.

One more time, slowly:

* fs/ramfs/inode.c does *not* optimise for rotating storage, what with having nothing whatsoever to do with any storage.

* it does *not* optimise for disc buffering, what with having no backing storage, disc or otherwise

* file cache (page cache, really) is just a mechanism for finding a page by offset in file. In case of object living entirely in RAM, that's exactly what you need to work with that object. Unless you want your objects to be contiguous in RAM, that is - great idea, that, for e.g. 800Kb text file. Or a 22Mb PDF document.

* Device drivers have nothing whatsoever to do with aforementioned ramfs.

* You have demonstrated just what is wrong with "visionaries". You keep making profound sounds without stopping to check whether they have anything to do with reality. Other than that of your bowel movements, that is.

As for being deliberately dense... I wouldn't have dared - any attempt to fake being dense would be simply pathetic next to the geniune article of that magnitude.

Preparing for nonvolatile RAM

Posted May 30, 2012 14:55 UTC (Wed) by daglwn (guest, #65432) [Link] (3 responses)

Thanks, Al. Real classy. It truly makes me want to learn more.

Preparing for nonvolatile RAM

Posted May 30, 2012 21:25 UTC (Wed) by Cyberax (✭ supporter ✭, #52523) [Link] (2 responses)

Well, you should.

Don't know about you, but after Al Viro's post I went and checked VFS source code - and he's entirely correct.

Preparing for nonvolatile RAM

Posted May 30, 2012 21:59 UTC (Wed) by daglwn (guest, #65432) [Link] (1 responses)

I'm sure he is correct. But he doesn't have to be an ass about it. He started right off with unwarranted sarcasm, graduated to foul language and it went downhill from there, leading to personal attacks.

I never claimed to be a "visionary." I'm far, far from that. The idea isn't even original, people have talked about it for years. It just strikes me that it makes a lot of sense given system architecture trends. Outright dismissal accompanied by foul language, holier-than-thou attitudes and outright insults says much more about Al than it does me.

Al definitely lost a notch or too on my respect ladder and that's a pity because I've generally enjoyed reading his posts/articles.

Preparing for nonvolatile RAM

Posted May 31, 2012 1:29 UTC (Thu) by bronson (subscriber, #4806) [Link]

I suppose the sarcasm is warranted if it's an idea that's proposed by many well-intentioned but ill-informed people. It attempts to keep the conversation short or, failing that, provide car-crash style entertainment. "Bring facts or suffer ridicule."

I'm no linguist but anybody who disagrees is a dweeb. :)