Messages in this thread | | | Date | Fri, 27 Feb 2004 23:00:44 -0800 | From | "Martin J. Bligh" <> | Subject | Re: 2.4.23aa2 (bugfixes and important VM improvements for the high end) |
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> 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.
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