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SubjectRe: Using %cr2 to reference "current"


On Tue, 6 Nov 2001, Alan Cox wrote:

> > "get_current" interrupt safe (ie switching tasks is totally atomic, as
> > it's the one single "movl ..,%esp" instruction that does the real switch
> > as far as the kernel is concerned).
> >
> > It does require using an order-2 allocation, which the current VM will
> > allow anyway, but which is obviously nastier than an order-1.
>
> I've seen boxes dead in the water from 8K NFS (ie 16K order-2 allocations),
> let alone the huge memory hit. Michael's rtlinux approach looks even more
> interesting and I may have to play with that (using the TSS to ident the
> cpu)

Btw, I also want to see what intense "for-optimization" high-order
allocators are going to do to the current VM.

Think about the possible intensive pressure (and CPU wasted) caused by,
for example, SCSI code which _always_ tries to do 1-order allocations (or
bigger?) to allocate scatter/gather tables. We want those allocations to
fail to 0-order allocations instead looping madly inside the VM freeing
routines.


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