Hello, all.
I know the function of the swap and can make swap partion or file.
But, if there is no swap partion at system, what would be happen?
that makes the system unstable or not?
I have one system that has no swap, but there was no problem until now.
Thanks in advance.
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2009/7/3 MontyRee chulmin2@hotmail.com
Hello, all.
I know the function of the swap and can make swap partion or file.
But, if there is no swap partion at system, what would be happen? that makes the system unstable or not?
I have one system that has no swap, but there was no problem until now.
Thanks in advance.
The swap file is there to provide extra memory when the physical RAM runs out. But if you have a lot (say 4GB+) ram in your machine, you may not even necessarily use swap. So, getting back to your question, it wont' cause problems - unless you run programs which consume more resources than the physical RAM in the PC.
At Fri, 3 Jul 2009 12:46:34 +0000 CentOS mailing list centos@centos.org wrote:
Hello, all.
I know the function of the swap and can make swap partion or file.
But, if there is no swap partion at system, what would be happen?
that makes the system unstable or not?
I have one system that has no swap, but there was no problem until now.
A swap partition is not essential to system operation so long as you have enough RAM. Most modern systems have more then enough RAM and can probably live without a swap partition .
Thanks in advance.
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CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
A swap partition is not essential to system operation so long as you have enough RAM. Most modern systems have more then enough RAM and can probably live without a swap partition .
True, but to answer the original question: If a system without a swap device needs to swap (and cannot) it will crash with an appropriate error message. Hopefully you would not get to that point; your processes should be killed when they run out of memory, but Linux's memory management scheme is not the simplest and you can run into issues where the kernel is unable to avoid a swapping situation.
-geoff
--------------------------------- Geoff Galitz Blankenheim NRW, Germany http://www.galitz.org/ http://german-way.com/blog/
On Fri, Jul 03, 2009 at 09:37:17AM -0400, Robert Heller wrote:
At Fri, 3 Jul 2009 12:46:34 +0000 CentOS mailing list centos@centos.org wrote:
Hello, all.
I know the function of the swap and can make swap partion or file.
But, if there is no swap partion at system, what would be happen?
that makes the system unstable or not?
I have one system that has no swap, but there was no problem until now.
A swap partition is not essential to system operation so long as you have enough RAM. Most modern systems have more then enough RAM and can probably live without a swap partition . -- Robert Heller -- 978-544-6933 Deepwoods Software -- Download the Model Railroad System http://www.deepsoft.com/ -- Binaries for Linux and MS-Windows heller@deepsoft.com -- http://www.deepsoft.com/ModelRailroadSystem/
In fact, my eeepc has 2 gigs ram and no swap. runs just fine. the only other thing I lose due to having no swap is the ability to hibernate.
2009/7/3 MontyRee chulmin2@hotmail.com
Hello, all.
I know the function of the swap and can make swap partion or file.
But, if there is no swap partion at system, what would be happen? that makes the system unstable or not?
I have one system that has no swap, but there was no problem until now.
Hate giving this answer, but "it depends."
You *can* run a system without page space, but you should really know what you're doing before you do this. It can work for types of workloads, but can get you into trouble in many situations.
If you do run without page space, you should configure the kernel overcommit options. You should also configure your application ulimits so that they behave more predictably in case they cannot allocate memory. You should also verify that your applications can properly handle a failed memory request.
To your question: For a well-known application, running without page space can make it more reliable *if* (and a big IF) all other applications are predictable. For example, say you're running you're well behaved application... Another process suddenly starts consuming memory. Your application then tries to allocate some memory. It cannot, so it crashes.
There are a ton of threads about how large the page space should be, given modern multi-gigabyte RAM spaces. There are threads about whether a page file or page volume is better. What's best will depend entirely on your workload and requirements :)
As your post demonstrates, a page-less system can run fine. The bigger your RAM space, the less likely you are to run into issues.
On Fri, Jul 03, 2009 at 02:18:57PM -0400, Kwan Lowe wrote:
If you do run without page space, you should configure the kernel overcommit options.
Is there a good, consistent, complete source of documentation for these options? They have changed a bunch in the 2.6 kernels, and I suspect the docs in the kernel source were not always up to date with the available options.
--keith
On Fri, Jul 3, 2009 at 11:11 PM, Keith Keller kkeller@speakeasy.net wrote:
On Fri, Jul 03, 2009 at 02:18:57PM -0400, Kwan Lowe wrote:
If you do run without page space, you should configure the kernel
overcommit
options.
Is there a good, consistent, complete source of documentation for these options? They have changed a bunch in the 2.6 kernels, and I suspect the docs in the kernel source were not always up to date with the available options.
I agree. Just doing a quick search and found that there's a bunch of outdated information and some that's not just outdated, but was never right in the first place.
For example, take a look at page volumes versus page files... Traditionally you would use a page volume because of the overhead involved with using files. Then changes to how page files were used made the difference almost (or completely) negligible. But then fragmentation may come into play when creating page files so page volumes would still be better.. But then storage is often virtualized so it again may not matter because the backing volume itself may be fragmented, or in some cases, reside on multiple physical volumes so it didn't matter. And with new allocation routines, maybe it again doesn't matter.
Here's one decent guide that explains what happens in an OOM situation:
http://www.linuxdevcenter.com/pub/a/linux/2006/11/30/linux-out-of-memory.htm...
There's also some good stuff on kerneltrap.org.
On 07/03/2009 05:46 AM, MontyRee wrote:
But, if there is no swap partion at system, what would be happen? that makes the system unstable or not?
That depends on what you're running. As people point out, you can usually get along without one, but doing so is a bad idea in some configurations. If you run a server that's dedicated to any single large application (like dedicated tomcat or database server), then you should have swap at least as large as RAM. Even when you configure the system so that applications stay within the bounds of RAM, fork() will fail in your application if it doesn't have room for a complete second copy of itself in memory. The space won't normally be used, since Linux uses a copy-on-write technique for fork(), but it still requires the space before it will allow fork() to succeed.
-
fred smith -
Geoff Galitz -
Gordon Messmer -
Keith Keller -
Kwan Lowe -
MontyRee -
Robert Heller -
Rudi Ahlers