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SubjectRe: andrea buffer code (2.2.9-C.gz)
On Wed, 19 May 1999, Manfred Spraul wrote:

>I noticed that you added a new spinlock to every memmap_t,
>i.e. 4 bytes for every 4096 bytes system memory.


>Is that really required? Have you made any profiling?

If you want to SMP scale well it's needed (I don't think on a two-way SMP
is a big issue having a per-memmap spinlock instead of a global spinlock
but on more powerful machines it can help I think).

The point is that there we don't need a global spinlock but there we can
scale far more finegriend on per-page basis. If our approch is to scale
well as possible in SMP without bother to waste some more kbyte of memory
the spinlock it's required. You know: to scale better you need to waste
more memory :-).

An UP compile done with a not-buggy compiler won't waste a bit of memory

>The spinlock is only acquired for a few lines,
>perhaps one global spinlock would save memory.

Yes but I am not worried, and being more finegrined in SMP is more fun :-).

Andrea Arcangeli

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