Re: 2.4.23aa2 (bugfixes and important VM improvements for the high end)

[Martin J. Bligh]

> The last issue that we may run into are apps assuming the stack is at 3G
> fixed, some jvm assumed that, but they should be fixed by now (at the
> very least it's not hard at all to fix those).

All the potential solutions we're discussing hit that problem so I don't
see it matters much which one we choose ;-)
 
> It also depends on the performance difference if this is worthwhile, if
> the difference isn't very significant 4:4 will be certainly prefereable
> so you can also allocate 4G in the same task for apps not using syscalls
> or page faults or flood of network irqs.

There are some things that may well help here: one is vsyscall gettimeofday,
which will fix up the worst of the issues (the 30% figure you mentioned
to me in Ottowa), the other is NAPI, which would help with the network
stuff.

Bill had a patch to allocate mmaps, etc down from the top of memory and
thus elimininate TASK_UNMAPPED_BASE, and shift the stack back into the
empty hole from 0-128MB of memory where it belongs (according to the spec).
Getting rid of those two problems gives us back a little more userspace 
as well. 

Unfortunately it does seem to break some userspace apps making stupid 
assumptions, but if we have a neat way to mark the binaries (Andi was
talking about personalities or something), we could at least get the
big mem hogs to do that (databases, java, etc).

I have a copy of Bill's patch in my tree if you want to take a look:

ftp://ftp.kernel.org/pub/linux/kernel/people/mbligh/patches/2.6.3/2.6.3-mjb1/410-topdown

That might make your 2.5/1.5 proposal more feasible with less loss of
userspace.

M
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