Re: Possible Idea with filesystem buffering.

Hans Reiser
2002-01-21T14:11:43Z

Rik van Riel wrote:

>On Mon, 21 Jan 2002, Hans Reiser wrote:
>
>>Pressure received is not equal to pages yielded. ... The number of
>>pages yielded should depend on the interplay of pressure received and
>>accesses made.
>>
>>Does this make more sense now?
>>
>
>Nice recipie for total chaos. You _know_ each filesystem will
>behave differently in this respect, it'll be impossible to get
>the VM balanced in this way...
>
>Rik
>
No, I don't _know_ that. Just because it got screwed up previously
doesn't mean that no one can ever get it right.

I think there should be well commented code with well commented
templates and examples, and persons who abuse the interface should be
handled like persons who abuse all the other interfaces.

Optimal is optimal, and if VM's default is seriously suboptimal for a
particular backing store then it simply shouldn't be used for that
backing store. Write clustering, slum squeezing, block allocating,
encrypting, committing transactions, all of these are serious things
that should be pushed by memory pressure from a VM that delegates. This
issue is no different from a human boss that refuses to delegate because
he doesn't want to lose control, and he doesn't have the managerial
skill that gives him the confidence that he can delegate well, and so
nothing gets done well because he doesn't have the time to optimize all
of the subordinates working for him as well as they could optimize
themselves. Rik, your plan won't scale. Sure, you have the time needed
to create one example template, but you cannot possibly create a single
VM well optimized for every cache in the kernel. They each have
different needs, different properties, different filessytem layouts.

Hans