Mailinglist Archive: opensuse (686 mails)

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Re: [opensuse] 64 bit vs 32 bit RAM consumption
Hello,

On Tue, 23 Jul 2013, Felix Miata wrote:
In googling the possibility of using a 64 bit kernel on an otherwise
32 bit openSUSE (consensus: don't try it), I found quite a bit of
mention of 64 bit apps using twice as much RAM? Is this true?

No. Pointers take twice as much. But see below.

Or is
it just misunderstanding arising from 64 bit using twice as many CPU
registers to increase its own speed?

On the contrary. Having more registers makes the program possibly
running faster. Completely independent from memory usage.

Or something else? My main system running 32 bit 11.4 has 4GB RAM and
is consistently using >50% of RAM for open apps, most of the rest for
disk cache, and always around 360MB unused. Would running 64 bit on
this system be consuming virtually all RAM for apps, leaving little
free for disk cache?

Nope. I used to run my usual stuff with 32bit, for years now with
64bit, and memory usage increased by maybe 10-20%.

FWIW, not all RAM is "cheap". To bring this DDR2 system up to its 8GB
max would cost ~$63USD. To replace its 2X2GB sticks with 2X4GB (to
free them for RAM upgrade to another system) would cost triple that.

Actually, since a while it's _quite_ simple: if your CPU is 64bit, use
64bit Kernels! You can _still_ run 32bit stuff if you install the
-32bit libraries that are needed. E.g. wine is actually just a package
that requires wine-32bit which requires the -32bit glibc, the libs for
X etc. You can also use i586 packages though they may conflict with
x86_64 packages.

A nice summary and a possible solution for you is described here:
http://en.wikipedia.org/wiki/X32_ABI

"the benefits of x86-64 (larger number of CPU registers, better
floating-point performance, faster position-independent code shared
libraries, function parameters passed via registers, faster Syscall
instruction... )"

Generally, x86_64 is as fast to significantly faster than i[356]86,
with only a slight memory overhead. And you can cut that down with the
x32-ABI. Though I do not know of any package in oS that uses that yet.

-dnh

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