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Rik van Riel on Kernels, VMs, and Linux
Andrea Scrimieri writes "
An Interesting
interview with Rik van Riel, the kernel developer, in which he talks
about the Linux's VM, particurarly about his own implementation (which was
recently adopted in Alan Cox's tree). With some controversy towards Linus
Torvalds.
"
I'm not so sure I agree with him -- if you want to make a dent in the market shares of Solaris and NT/2000/XP you have to keep up with their innovations (Async-I/O, better SMP, etc.). As a user of Linux as our OS of choice for our database and web servers I am feeling a lot of pressure to switch to Solaris because of their better handling of higher-load environments (OLTP databases, web servers, etc.). If Solaris wasn't so damn expensive we'd probably be using SunFire 280's. So I'm pleading to keep up with the big dogs so that I can be reassured that Linux has what it takes (it's handling things fine now but as he said in the article, everyone needs more RAM, CPU, etc.).
Thanks,
--
Matt
I think it was an excellent decision of Linus to remove Rik's VM from the mainline kernel. If not for technical reasons then for political reasons.
Rik's VM obviously needed to be fixed and/or tuned, but apparently lacked the necessary attention from Rik. If Linus had not removed the VM, it would probably have been the situation for a while. Instead we now have TWO VM's which are rather stable and Rik working full speed to make his VM the best.
Competition is good! Which VM will be the best for the future will be determined by Survival Of The Fittest(tm)
It can be argued though, that it was not the right time during 2.4, but Andreas VM seemed to stabilise rather quick with the high level of attention to the problem. Sometimes it takes drastic measures to get results...
I think this kind of infighting is great, as long as it doesn't get out of control.
We get to see arguments and competing subsections of the kernel - this is SO one of the most underrated benefits of open source. Users of some other OS's don't have this benefit. I am not a programmer, so to me, I don't really understand/care the benefits of different VM systems, but I know that some other, smarter people do, and they're all trying to figure out the best way to do it, and that's good enough for me.
I say let them go at it, let the best code win - it can only help us. And who cares how MS construes this, I'd like to see them open up their development model and see what kind of conflicts they are having.
OT - but kerneltrap.org has a good interview with Alan Cox today....
this kind of bashing between the high priests of Linux is not good
/. Linus is not an all knowing genius. He makes mistakes. Perhaps this is one of those mistakes. The real question is whether the benefits of the stewardship he provides compensates for the hindrances his authoritarianism creates.
Sure it is. How else are we going to find out where our disagreements are and work through them? Or, at the very least, learn not to make the same mistakes in future projects. The problem of the Linus bottleneck has been known for a long time. This "bashing" is not new, it's just current.
Having Linus Torvalds around helps insure that, for the average user, there is no splintering of development effort -- just use the Linus kernel. But it also severely hinders improvement because you are limited to what Linus likes or dislikes.
And despite what may be the common conception on
I have a lot of respect for Rik van Riel, but I think that Linus made a good decision to "cut bait" on his VM implementation for 2.4.
It was not that Rik's ideas were bad, it was just that their complexity and implementation were going to take too long - they should have been hashed out in 2.3 instead of 2.4.10.
I'm looking forward to having Rik prove his reverse mapping technology implementation in 2.5.
May the best ideas ultimately win, and may the giants of the kernel not take offense at each other. It would be a real shame if something stupid like Linus' lossy source code control system put off Rik so much the Linux community at large lost his wonderful contributions.
Here's to hoping that Linus gets more sensitive in some cases, and that Rik gets less sensitive in some cases.
"Provided by the management for your protection."
Maybe we need some help from *BSD VM hackers to to solve this VM thing.
Since a year and it still has big holes.
Recall that "Linux" is owned by Linus. It's not inconceivable to envision a pissing match of the egos ending in "Cox' "rogue" kernel isn't true Linux. Rename it." one day.
Trolling is a art,
Rarely does one person have a monopoly on good ideas, so it's inevitable that finding the right solution will come from competition between more than one good idea. So long as progress continues, as it has, this is healthy. Both Mr. Torvalds and Mr. van Riel recognize that they are "stubborn," and both seem to deal with the heat fairly well.
end of line
Then again, how much is RAM? I just bought 512MB for less than $40. I NEVER swap (running ~800MB RAM / server) and never want to. I ran my first e-commerce web site w/ SSL and mSQL on a 486SLC-20MHz with 5MB of 110ns DRAM. Yeah, it swapped. But these days, most machines are way overkill for serving web pages, files, and queries.
----- Refactoring is the reason why man does not mistake himself for a god.
Yes, such a thing would be appreciated. It's all very well developing linux in order to "improve itself" but one can take the "stuff the users" approach too far.
The problem is that there isn't a decent multi-patch versioning system out there: how would you tell CVS you wanted to store versions of files pertaining to 2.5.2-mjc and 2.4.13-ac1 and 2.4.18 and then a set of files for Rik's VM? Then how on earth would you pull out the set of files that constitutes a `linus+mjc' tree, or a `linus+ac' tree, from what you've stored?
~Tim
--
Rushing on down to the circle of the turn
I strongly feel that honesty wins in the end, because people aren't stupid. No one believes that IBM or Microsoft is one happy camp singing "we are the world."
It's great there is a lot of attention on the VM and intense effort to make it better. I have no doubt linux and Rik are professionals and have no problems putting politics aside to get the job done. That is after all part of being a professional. Rik makes some good argument and given enough time and money he'll build the VM of his design. Will it matter 10 years from now? Most likely not. Development will continue and linux will get better. Butting heads is part of the fun, because without conflict people tend to stagnate.
I've been wondering that myself. It's just work to do but it shouldn't be rocket science. Of course a number of people are concerned about the code size as is, you can't just add a new branch of code every time there is a conflict and pack them all together. This does seem like a somewhat good case for it.
BTW, this kind of bashing between the high priests of Linux is not good. You can bet your bottom dollar that MS is going to use this conflict to fuel their propaganda machine, saying Linux is a fractious OS run by a bunch of young upstarts who can't agree on anything.
No this is a good thing. Most of the linux kernel hackers have egos the size of small countries, and that's a good thing because they take pride in their work. Most of them also work as professionally and egolessly as I have ever seen. They can get in fights and then deal with it and keep working. This is far better than the closed world where people get in fights and take it personally and then try to react in some way. I've seen project where people were trying to fail the project to get revenge on someone on the team or managment for something stupid they did in the past. In the linux world people get in fights and everyone can see and they react accordingly, sometimes being told that you're being an ass is a good thing when you're being an ass, sometimes having people stop talking to you for a few days is a good thing, and sometime people appologize and that's a good thing. It's not behind closed doors though and it's hard to undermine things when it's all in the open. There is also some insanely good discussion on certain things some times. There is also something to be said for defending ideas and the strength they have when you can defend them in public.
Label this a flame if you want but I was absolutely disgusted by the tone and tenor of Rik's responses in that article. Regardless of the technical merits of his code or algorithms, Rik's repeated attacks on Linus will certainly not move the operating system forward.
When the author of the article ended with "Thank you for your kindness and the opportunity to get to know you better", I almost fell out of my chair laughing. The only thing that stopped me was that Rik's behavior really isn't funny. It isn't professional and it has no place in the open source or any other community. It speaks volumes about Rik's emotional maturity or more accurately his lack thereof.
An honest environment -- such as fostered by "free" software -- is both good and bad. On one hand, I (as a programmer) am comforted to read the kernel mailing list and other resources that let me know exactly what is happening with my tools. I don't need to wonder what's happening with "free" software -- and this is more comforting to an engineer like myself than is the closed-door, silence-is-golden, hide-the-bugs policy of a Microsoft.
On the other hand: Show this interview to an MIS manager who need 24/7/365 reliability, and she is going to be very nervous about deploying a Linux-based solution. You can talk until you're blue in the face about reliable distros and the open road to sofwtare quality -- what the MIS/corporate person sees is chaos and feels a lack of COMFORT .
"Out of sight, out of mind" is a philosophy many people adhere to, especially when dealing with complex issues they can not or do not want to grasp. From waste storage in Nevada to the the war in Afghanistan, most people lack the time and initiative to understand what is really happening; they go on appearances and marketing, and ignore complex and disturbing facts.
Technology is no different. The MIS manager doesn't want to hear about VM conflicts or file system bugs or different kernels -- such issues are beyond their capability and desire to understand. Buying Microsoft is (or was, until recently) comforting, because no one ever saw the internal debates and code battles and what-not that any development team expresses. Even recent security disclosures about WinXP are unlikely to shake the faithful -- but those same people will run in fear from the blunt honesty of Linux.
Ignorance may be bliss, but it can also get you killed. I know people whose lives depend on cars, but they have no knowledge of how to check the oil. Most MIS managers simply want to drive software; if it looks good (like a Jeep Liberty), they don't pay attention to whether it is safe (the Liberty performs poorly on crash tests).
I doubt, however, we're going to change human nature -- and I'd rather have spirited debate and even some nasty contention if it means that people are striving to make Linux the "best" it can be.
All about me
It started out with Rik's VM in the kernel, since it was a promising new development. However, once it was in Linus's kernel, the fact that Rik's development style was not compatible with Linus's source control style because an issue, because the VM wasn't getting updated in Linus's tree.
So Linus switches to the other VM, which is based more on the original. This means that Rik can do his development without dealing with Linus and the Linus tree can have an up-to-date VM. When Rik's is to the point where he's really happy with it and he doesn't think he'll have to make a lot of patches (and it does all the things he wants), it will probably go back in.
Since then, Rik and Linus have figured out (hopefully) how their interaction failed to work, and what Rik has to say along with his patches to make Linus know they're worth looking at. It turns out that it is possible to automate this process, such that a script will send the patches when appropriate, with the right assurances of freshness (having actually tested them, of course).
Linus wants to be able to ignore any patch that isn't for the part he's thinking about at the time (e.g., non-block-i/o patches around the beginning of 2.5). When it becomes interesting again, however, the original patch may not be right any more. Having not looked at the patch at the time when it was sent, Linus can't determine whether it is still good, since the author may have found bugs, and he doesn't know exactly what the patch was supposed to do. He wants the author to make any updates needed and resend it. It may be, of course, that the patch doesn't need to be changed, and the author doesn't have a new and better patch, but Linus can't tell unless the author sends it again with a note that it's still good.
So Rik's patchbot will test whether the patch still applies and still works, and has not been replaced by a new version, and then will send it again until Linus actually looks at it. This seems to me like a good plan, since it doesn't require Linus to test everyone's old patches and have a complicated mail system. And Linus won't accidentally apply the wrong version of a patch or be unable to find a patch.
...how a lot of kernel developers seem to talk mainly about how well their patches help a server withstand slashdotting? ;)
I mean... look at that bloke who posted a scheduler patch in Kernel Traffic, and now Rik... both mention a certain website. I dunno if this is a good or bad thing
A VM is basicly a small thing: a list of pages, every page has a set of properties and an interface on top of that to get things done with the pages (claim/free/mark dirty etc). I wrote one on an MSX2 in 1986 for having 256KB roms in 128K ram + 128K vidram (and 32K disk :)). Of course, modern OS-es need a VM that can take decisions, is scalable on different hardware, and can handle the requests fast.
A lot of research has been done on virtual memory and the managercode for this type of memory. Also a lot of different types of VM's are implemented in different OS-es, all with pro's and con's in different situations. It's therefor not hard to dig in and get the knowledge you need.
F.e.: the rmap stuff is a nobrainer. If you let the VM handle every request to share/allocate a mempage, that VM can keep a set of pid's per page. IIRC NT's VM (VMM32) does this. That the current VM in Linux doesn't already have this feature is beyond me.
Never underestimate the relief of true separation of Religion and State.
>> The Linux kernel is starting to look like anarchy to non-developers.
What data points do you base this observation on? You believe that there is an appearance of linux kernel development becoming increasing chaotic?
You are very wrong. A true analysis of the progress of linux kernel development would show a measurable decrease in the level of chaos in the system.
The past few years have seen an increase in paid full time linux kernel hackers. These hackers are generally tasked with working on a specific sub-system and/or providing source control management. The Marcelos and Coxes of the world are increasing in number and their work is really paying off in a more ordered kernel development process.
Even the volunteers like the kernel janitors work in a more structured and orderly manner.
Perhap someone should write a white paper detailing the main kernel hackers and the evolution of the kernel development process. THAT would make for good PR.
If your process was allowed to exist in the first place, it should not be killed by the VM system.
So we know before a process gets to execute exactly what its memory usage profile is? A VM is called upon to predict the future all the time, but this is ridiculous. I can understand that we'd rather not start a process if we're going to kill it off later, but just how are we supposed to make that determination? I've got 3/4 of my memory free. Of course the system will let me start another process --we're nowhere near OOM. But the new process proceeds to allocate and allocate and allocate... And now we really are OOM. What now? What have we solved?
The worst that should happen is that it gets suspended with all of its pages taken away.
"taken away"? Where do they go? You obviously can't drop them on the floor if you're planning to unsuspend the process at some point. You can drop the executable pages, but if we're in an OOM condition we've already done that. And we're out of swap, so we're not putting the pages there, either.
If there are other processes waiting for the one that's suspended, then eventually they'll go to sleep, their pages will be released, and the suspended process will wake up.
Now *that* is a chain of events which makes absolutely no sense to me. I repeat: *We* *are* *OOM*. Where do their pages go and how, exactly, does this allow the VM to make some progress without deadlocking the system?
Color me skeptical.
I don't want to get marked down or flamed for trolling or anything, because I am not:
Thanks for posting this quote. The more I read in to this stuff, it often times seems as though Linux has an immature attitude, and often acts like a baby. Ignoring patches because you have a disagreement from someone is just plain immature. I can see how frustrated I would get working with Linus. He still acts like it is his little baby project, and that is just not the case anymore. Thosands of developers are working on it, and this kind of attitude by Linus would just turn people off from the project.
These kind of snide remarks by Linus are not needed, and if I was Rik, I would tell Linus to fuck off and put my talent to use somewhere else. Linus, act a little more mature.
Moon Macrosystems. Sun's biggest competitor.
Yes you are trolling! Especially since the original poster could not get the quote right.
..."
... who is being immature now?
Linus wrote: "...Which, btw, explains why I don't consider you a kernel maintainer, Rik,
See for yourself!
The reason was that Rik didn't care about everybody else if his bugfixes were not applied. Would YOU like a maintainer that didn't care about the rest of the world?
"I would tell Linus to fuck off"
First off, you need to study your own subject line: OOM Killer. OOM means out of memory. It does not mean low memory; it does not mean "maybe the admin can link in some more swap;" and it does not mean "move pages into a protected buffer." It means out of memory: there is no memory left. Anywhere.
You say:
then you say:
Make up your mind dude -- which side are you on? Hint: Your second statement is correct, sarcastic as it was. We can't know the true memory behavior of a process ahead of time, so we can't block processes that are going to become too large.
Next you say:
Those pages contain data, they cannot be taken away. The must be moved somewhere
Ah, your fingers are moving, but you don't understand the words. This is still swap space; the label is meaningless. And if we have swap available, then we're not out of memory, are we? This is a low memory condition, and is irrelevant to this discussion.
Okay, so how about:
Once again, you use the term without understanding it. This is called memory (as you said,) and if there's some left, then we're not out of it, are we? Once again, this is a low memory condition, and is irrelevant to this discussion.
This next statment needs to be pulled apart, as you try to make two points with it:
Agreed, but we're not talking about "extreme VM load", are we? We're talking about out of memory conditions. No memory left. Anywhere.Sure, but these systems have been hand-tuned to avoid running out of memory in the first place. Is this a good thing? Let's see:
Oddly, you first said "must die," but now say "no need," but I'm willing to ignore that. Ideally, a system should never run out of memory. But how can you know your machine is safe? After all, you can never know the memory requirements of a program ahead of time. So you can either throw excessive amounts of resources at your machine, or you can add support for low-memory and out-of-memory conditions. Your ideas for low-memory problems may be good, but they're not relevant here.
So the only question is this: Is an OOM killer worth the effort? OOM killer performs a partial system shutdown, allowing reletively quick recovery. This might be valuable for servers, but for single-user computers, it's usually easier to just reboot, especially since the machine will be desperately thrashing by that point.
Is an OOM killer worth writing? We're not paying Rik, so that's up to him. If you want low-memory conditions handled better, pay up, or write it yourself.
Look in the mirror, dude -- that's you!
-B
Not that this wasn't entirely predictable.
There's a lot of back-and-forth discussion, not only on the VM, but on the feature (un)freeze of 2.4/2.5, and on how Linus is a lousy patch control system. But maybe that's not the most important thing here.
Way back when, the purpose of a development kernel was to feed things in to a stable kernel tree. Now part of the problem has to be that Linus started 2.4 way before 2.3.X was ready for it, but it looks like history is repeating itself. 2.4 isn't all that stable, even now, but Linux is happily accepting lots of new goodies to play with in 2.5.
Something is not working right here. Is Linus less demanding of quality now, since he's willing for somebody else to come in and fix up the allegedly stable kernel tree? Or is he accepting too many things to allow a development tree to stabilize?
I suspect it's a combination of too much stuff and too big a kernel. Instead of the heady days of 2-3 kernels per week in the development tree, and the stable tree gets another kernel every week or two, now we have a development kernel every week or two and a stable patch every month or three. And the kernel size is 10x bigger than in the 1.0 days.
Look how long it took the USB stuff to filter through the development into the stable tree.
It seems obvious the Linus Linux development process is not scaling. I'm not sure what the answer will turn out to be, but it may be some combination of the following:
(1) More "boutique" kernels like Alan Cox's ac series, feeding into the "stable development" kernels that Linus has been generating.
(2) More formal check-in methods, a la CVS commit. This may take some developer training in how to use CVS -- does anyone want to offer Linus a course and set up a server for him? I bet he'd take a complementary Geek Cruise!
(3) Some kind of more rigorous control in the stable kernel tree. I suppose you could say Redhat and SuSE are doing this informally now; if they start coordinating their efforts, and get IBM involved, the kernel will be incredibly stable. And even more incredibly slow to update.
(4) More beta testers to crack the newer kernels. This is going to get harder, as more of us need to get work done on our Linux boxes. It used to be a hassle when Linux crashed; now it's not acceptable any more!
(5) Better ways for these users to track down problems and report bugs. This last week I heard myself say, "Try rebooting your Linux box and see if the problem goes away." I just don't have the time, energy, knowledge, and skills to deal with lusers' "I've got a problem" whines any more.
(6) Is the quality of kernel patches too low? Do we need to develop some regression tests for the kernel, which a patch would have to pass before it would be accepted? (And how do you do a regression test program of this magnitude without Microsoft's beta testers, AKA customers?)
Anybody want to contribute more ideas to the list? We can spam Linus with them until he agrees!