[OT] highmem

On Wed, Apr 02, 2008 at 10:08:07AM +0800, jam wrote:
> Now the world gets tricky: For 1G RAM and over you should be
> running a 64 bit system.

The "real" barrier runs around 3G practically and 4G
semi-theoretically (that's where one needs PAE which
is even slower than HIGHMEM4G used for RAM over 896M;
usually 4G-without-PAE results in memory amount being
available to the system anywhere between ~3.3..3.7G
since different layouts and holes kick in, changing
with motherboards and BIOS revisions at times).

2G is pretty OK even with standard HIGHMEM4G in 32-bit.

> If you look technically how BIGRAM works you will see that
> despite everyone's opinions whichever way 64bit is the only
> option.  This is especially true with ThinClients where
> simultainious apps are running as opposed to 'lots of serial
> apps' which is better suited to BIGRAM. 

Not with 6 clients and 2G RAM.  Folks run ~100 clients on 8G!

And 64-bit isn't definitely faster/easier than 32-bit: one gets
multiple architectures at once, with troubles like adobe flash
which are harder to fix when things are working; performance-wise
one gets more registers and faster/better memory access but there
are corner cases as well, e.g. 2x longer pointers making cpu
caches less efficient in case things are falling over to
higher-level cache or even out of any.

I've seen "usual" +/- 7--20% difference numbers with notable
exception being OpenSSL doing 3x better on x86_64 than on x86.

> So IMHO you do not give good reason for local apps.

+1

-- 
 ---- WBR, Michael Shigorin <mike-u2l5PoMzF/[email protected]>
  ------ Linux.Kiev http://www.linux.kiev.ua/

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