Comments on: 32bit or 64bit for My Low End VPS, Take #2

By: James

James — Mon, 01 Aug 2011 04:50:25 +0000

I am trying to choose the os template. thanks for the post. So 32bit is good for low end. what if I upgrade later to high end vps? 32bit will still work fine??

By: LowEndAdmin

LowEndAdmin — Sun, 20 Mar 2011 22:43:34 +0000

Yes I don’t deny that. Specific programs tuned for 64bit can get quite a bit of performance gain, especially those using 64bit arithmetic and 64bit registers. At the same time 64bit code is a bit bigger so your performance might suffer if a loop cannot be fit into cache.

I guess people just need to weight out what architecture is most suitable for his/her applications. You are trading memory for arithmetic performance. Sometimes it’s worth it, and sometimes not.

By: dd

dd — Sun, 20 Mar 2011 17:04:44 +0000

“But the main reason for going 32bit is, your applications are going to use far less memory due to a lot of data is only stored at 1/2 the space as 64bit. ”

While this is true there are speed advantages to 64 bit:

1) 64 bit integer math (such as used in encryption algorithms) is done in hardware not software.
2) The number of general purpose registers is 8 for 32 bit (eax, ebx, ecx, edx, ebp, esp, esi, edi) wheras it is 16 for 64 bit (rax, rbx, rcx, rdx, rbp, rsp, rsi, rdi, r8, r9, r10, r11, r12, r13, r14, r15) so it is possible for the compiler to keep more variables on registers which are faster than the stack.
3) More arguments can be passed in registers for small functions than pushing them on the stack.

These points make the same program faster when compiled as 64 bit than when compiled as 32 bit though it may use more memory it will make it up in speed.

By: Sidahmed

Sidahmed — Thu, 09 Sep 2010 16:05:45 +0000

Thanks very much Ron for the clear and detailed answer, I appreciate it.

By: Ron

Ron — Thu, 09 Sep 2010 15:43:47 +0000

@Sidahmed – Generally if you’re running a 32bit OS on Xen (Paravirtulized) then I would highly recommend that you ask the provider to enable PyGrub for you so that you can use the 32bit Xen kernel on your OS.

On the other hand, if the provider does not offer PyGrub, then you are better going for a 64bit OS as it will likely cause less compatibility problems.

For example, various installation scripts check the kernel architecture to determine if to install 32bit or 64bit packages. If you were running a 32bit on a Paravirtulized OS on a 64bit host node, without PyGrub, the install script would then think you were running a 64bit OS, try to install the 64bit packages, and fail to do so.

By: Sidahmed

Sidahmed — Thu, 09 Sep 2010 13:14:45 +0000

Sorry, I mean what about Xen? (about is missing from the above comment)

By: Sidahmed

Sidahmed — Thu, 09 Sep 2010 13:13:24 +0000

@bekanosky has confirm that “there is no problem running 32bit guests on 64bit OpenVZ system”.
What Xen, does is recommend to run 64bit OS on a VPS that hosted on 64bit node? I need someone to confirm what QuickWeb-Joe (Comment #2) has wrote.

By: LowEndAdmin

LowEndAdmin — Mon, 26 Jul 2010 08:41:26 +0000

@bekanosky — there is no problem running 32bit guests on 64bit OpenVZ system. The burstable/guaranteed memory also only counts the memory used in the userland, i.e. your 32bit apps. All the kernel portion of your apps will be counted against kmemsize in OpenVZ, and most sensible providers will give you a very large allowance on that so mostly irrelevant.

I guess not only process that consume memory, something else will consume too. Need to digging more.

For OpenVZ, it is mostly processes and their related resources (shared memory, opened files, TCP connections, etc). On Xen your kernel memory is counted against your allocated amount + cache/buffers and lots of other cryptic stuff that you can check under /proc/meminfo. Very different ball game.

By: bekanosky

bekanosky — Mon, 26 Jul 2010 06:02:32 +0000

Another question. Our user process living inside the kernel, right ? The kernel itself use 64bit.So, our process is in 64bit mode.

LEA:”However if you are comparing the same distro on the same virtualization platform, 64bit is still using more memory than 32bit.”
I guess not only process that consume memory, something else will consume too. Need to digging more.

– afterall, i’m just another VPS newbie –

By: bekanosky

bekanosky — Mon, 26 Jul 2010 05:41:56 +0000

“For example the contained processes may be 64 bit and use multiple cpus, if the host is 64 bit and has multiple cpus” -> how about this statement.
But, maybe you’re right. Don’t try this yet at 64bit openvz.

By: LowEndAdmin

LowEndAdmin — Mon, 26 Jul 2010 05:35:10 +0000

Well. Your research is on comparing Xen vs. OpenVZ, rather than 32bit vs. 64bit. OpenVZ uses a completely different memory accounting system, where your burstable memory/privvmpages is probably the single most important metrics. Applications on VZ that allocates more than it uses (kernel-level overcommitting) imply that you probably will not be able to run as many applications if not tuned properly — issues that are not relevant to Xen/KVN/VMWare-based VPS.

However if you are comparing the same distro on the same virtualization platform, 64bit is still using more memory than 32bit.

By: bekanosky

bekanosky — Mon, 26 Jul 2010 05:29:27 +0000

I have made some *simple* research about this 32 bit issue.
It is obviously not a real research.
My conclusion is, what’s really matter in openvz is your host kernel/distro, not your distro/kernel.

http://en.seputarvps.info/blog/openvz-user-bad-news-32bit-distro-will-not-save-your-memory/

And i think Xen PV without own kernel will be the same.

By: KLIKLI

KLIKLI — Sat, 17 Jul 2010 14:37:13 +0000

Is somebody “stealing” my name?!
@bekanosky Sorry I was confused.

By: bekanosky

bekanosky — Sat, 17 Jul 2010 13:46:28 +0000

@KLIKLI
?????
i don’t use webmin

By: KLIKLI

KLIKLI — Sat, 17 Jul 2010 05:15:08 +0000

@KLIKL that was me.

Mine is sitting in 79-85 mb RAM use right now. My php config probably could use some optimization though. Also, this is 64 bit CentOS on OpenVZ as 64 bit is the only option for CentOS.

By: KLIKLI

KLIKLI — Sat, 17 Jul 2010 04:01:05 +0000

@bekanosky
Isn’t you said that turning off webmin saved 20MB memory?

By: bekanosky

bekanosky — Fri, 16 Jul 2010 22:52:52 +0000

@KLIKLI
memory usage is 40MB-50MB.

By: KLIKLI

KLIKLI — Fri, 16 Jul 2010 17:37:56 +0000

@bekanosky

Good :D you did make a great website with low generation time

By: bekanosky

bekanosky — Fri, 16 Jul 2010 16:39:32 +0000

@KLIKLI
Yes, it is real wordpress blog.
Just click on my name to see the action

By: KLIKLI

KLIKLI — Fri, 16 Jul 2010 03:20:35 +0000

@bekanosky

Are you serving real websites on your VPS? How is the memory usage?

Anyway I would say burstable RAMs should not be calculated in your “Usable RAMs” list.