Is it possible to put an artificial limit on the amount of memory a .NET process can use? I'm looking to simulate low-memory situations for testing purposes.
Right now we use a virtual machine for this type of thing. It works, but I'm curious to know if we can figure out a more convenient approach. One that could easily be automated would be ideal.
Edit: As Hans Passant points out, just limiting the amount of virtual memory available to the process won't replace the VM-based tests. The tests are for performance, so I would need to get swapping instead of OutOfMemoryException.
One that could easily be automated would be ideal.
You can use Windows Job Objects to manage this from code. Processes can be associated with a job, and JOBOBJECT_BASIC_LIMIT_INFORMATION allows you to restrict the working set size.
Alteratively, you can call SetProcessWorkingSetSize on the process directly, which will restrict the maximum allowable memory usage for that process.
The windows Application Verifier tool can simulate low resource levels, like low memory: http://msdn.microsoft.com/en-us/library/aa480483.aspx
A more programmatic solution using job objects (as #ReedCopsey also suggests) is here: http://www.codeproject.com/Articles/17831/How-to-Set-the-Maximum-Memory-a-Process-can-Use-at
Right now we use a virtual machine for this type of thing
Which probably means you limited the amount of RAM. That's not much of a test, a Windows process can never run out of RAM. You'll just slow down the process, the operating system will be swapping pages more frequently.
The real limitation is available virtual memory address space. Which is a fixed number for a 32-bit process, 2 gigabytes. Give or take a few non-standard options to increase that number. An OutOfMemoryException tells you that the process doesn't have a hole left in VM big enough to fit the allocation.
You can limit the amount of VM space by simply allocating a bunch of 50 megabyte byte[] arrays and storing them in a static variable of type List<byte[]> at the beginning of Main().
Related
I have a .NET process that, for reasons I will not go into, consumes a large amount of RAM. What I want to do is implement an upper limit on the amount of RAM this process can use. Is there a way to do this?
The closest I have found is Process.GetCurrentProcess().MaxWorkingSet which I don't think does what I want based on the documentation I have read.
The best I have come up with is using GC.GetTotalMemory(true) to get the amount of RAM being used and restart if it is over a certain amount. But this is not ideal.
You can set the minimum and maximum sizes of the process's working set by calling SetProcessWorkingSetSizeEx or SetProcessWorkingSetSize.
There is a pinvoke.net entry for SetProcessWorkingSetSize.
Be sure to read the MSDN documentation for whichever function you decide to call.
Note that this doesn't prevent your application from allocating more virtual memory, but rather puts limits on how much physical RAM the process's virtual memory occupies at any given time.
Im a little confused with regards to the memory limitations of an application. As far as i can see, if i write a c# application, targeting x64, my program will have access to 8TB of Virtual address space = space on the HD?
OS >= Windows 7 professional supports 192gigs of RAM. So if i had 192gig system (unfortunately i dont), i could load just over 8.1TB of data into memory (assuming no other processes were running)?
Is virtual memory only used when i have run out available ram? Im assuming there is a performance implication associated with virtual memory vs using RAM?
Apologies if these appear stupid questions, but when it comes to memory management, im rather green.
Your question is actually several related question, taking each individually:
OS >= Windows 7 professional supports 192gigs of RAM. So if i had 192gig system (unfortunately i dont), i could load just over 8.1TB of data into memory (assuming no other processes were running)?
No, it would still be 8 TB. That is the maximum amount of addressable space, whether it is in RAM or elsewhere.
However you could never have 8 TB in use, even if you some how unloaded Windows itself, as the OS needs to keep track of the space being used. In total, you could probably get to 7 TB approximately.
is virtual memory only used when i have run out available ram?
No, if you have virtual memory turned on the entirety of RAM is typically preloaded onto your HDD (give or take a few seconds). This allows the OS to unload something to make room if it feels the need, without having to persist the data. Note that the OS keep thorough track so will know if this is the case or not.
Im assuming there is a performance implication associated with virtual memory vs using RAM?
Depends on your context. Every seek on the hard drive takes a computational eternity, however it is still a fraction of a second. Assuming your process isn't thrashing and repeatedly accessing virtual memory, you should not notice a significant performance hit outside high performance computing.
Apologies if these appear stupid questions, but when it comes to memory management, im rather green.
Your main problem is you have some preconceived notions about how memory works that don't line up with reality. If you are really interested you should look into how memory is used in a modern system.
For instance, most people conceptualize that a pointer points to a location in memory, since it is the fundamental structure. This isn't quite true. In fact the pointer contains a piece of information that can be decoded into a location in the addressable space of the system, which isn't always in RAM. This decoding process uses quite a few tricks that are interesting, but beyond the scope of this question.
Normally, you should write applications targeting Any CPU. The .NET loader then decides (depending on the platform it is running on) which version of the run-time environment will execute the application and into what kind of native code it will be compiled. There is no need to specify the platform, unless you are using custom native components which will be loaded into the process created for your application. This process is then associated with some virtual address space - how that is mapped to physical memory is managed by the OS...
We have a 64bit C#/.Net3.0 application that runs on a 64bit Windows server. From time to time the app can use large amount of memory which is available. In some instances the application stops allocating additional memory and slows down significantly (500+ times slower).When I check the memory from the task manager the amount of the memory used barely changes. The application keeps on running very slowly and never gives an out of memory exception.
Any ideas? Let me know if more data is needed.
You might try enabling server mode for the Garbage Collector. By default, all .NET apps run in Workstation Mode, where the GC tries to do its sweeps while keeping the application running. If you turn on server mode, it temporarily stops the application so that it can free up memory (much) faster, and it also uses different heaps for each processor/core.
Most server apps will see a performance improvement using the GC server mode, especially if they allocate a lot of memory. The downside is that your app will basically stall when it starts to run out of memory (until the GC is finished).
* To enable this mode, insert the following into your app.config or web.config:
<configuration>
<runtime>
<gcServer enabled="true"/>
</runtime>
</configuration>
The moment you are hitting the physical memory limit, the OS will start paging (that is, write memory to disk). This will indeed cause the kind of slowdown you are seeing.
Solutions?
Add more memory - this will only help until you hit the new memory limit
Rewrite your app to use less memory
Figure out if you have a memory leak and fix it
If memory is not the issue, perhaps your application is hitting CPU very hard? Do you see the CPU hitting close to 100%? If so, check for large collections that are being iterated over and over.
As with 32-bit Windows operating systems, there is a 2GB limit on the size of an object you can create while running a 64-bit managed application on a 64-bit Windows operating system.
Investigating Memory Issues (MSDN article)
There is an awful lot of good stuff mentioned in the other answers. However, I'm going to chip in my two pence (or cents - depending on where you're from!) anyway.
Assuming that this is indeed a 64-bit process as you have stated, here's a few avenues of investigation...
Which memory usage are you checking? Mem Usage or VMem Size? VMem size is the one that actually matters, since that applies to both paged and non-paged memory. If the two numbers are far out of whack, then the memory usage is indeed the cause of the slow-down.
What's the actual memory usage across the whole server when things start to slow down? Does the slow down also apply to other apps? If so, then you may have a kernel memory issue - which can be due to huge amounts of disk accessing and low-level resource usage (for example, create 20000 mutexes, or load a few thousand bitmaps via code that uses Win32 HBitmaps). You can get some indication of this on the Task Manager (although Windows 2003's version is more informative directly on this than 2008's).
When you say that the app gets significantly slower, how do you know? Are you using vast dictionaries or lists? Could it not just be that the internal data structures are getting so big so as to complicate the work any internal algorithms are performing? When you get to huge numbers some algorithms can start to become slower by orders of magnitude.
What's the CPU load of the application when it's running at full-pelt? Is actually the same as when the slow-down occurs? If the CPU usage decreases as the memory usage goes up, then that means that whatever it's doing is taking the OS longer to fulfill, meaning that it's probably putting too much load on the OS. If there's no difference in CPU load, then my guess is it's internal data structures getting so big as to slow down your algos.
I would certainly be looking at running a Perfmon on the application - starting off with some .Net and native memory counters, Cache hits and misses, and Disk Queue length. Run it over the course of the application from startup to when it starts to run like an asthmatic tortoise, and you might just get a clue from that as well.
Having skimmed through the other answers, I'd say there's a lot of good ideas. Here's one I didn't see:
Get a memory profiler, such as SciTech's MemProfiler. It will tell you what's being allocated, by what, and it will show you the whole slice n dice.
It also has video tutorials in case you don't know how to use it. In my case, I discovered I had IDisposable instances that I wasn't Using(...)
is there anyway i can have my application tell how much memory the user has and if the application is getting close to taking up a high percentage of that.
also, how do you know how much memory the machine gives to OS, video cards, etc . .
for example, if you have 4gb of memory, how much actual memory is given to applications, can you configure this.
is there anyway i can have my application tell how much memory the user has and if the application is getting close to taking up a high percentage of that.
Yes, it's possible (see some of the other answers), but it's going to be very unlikely that your application really needs to care. What is it that you're doing where you think you need to be this sensitive to memory pressure?
also, how do you know how much memory the machine gives to OS, video cards, etc . .
Again, this should be possible using WMI calls, but the bigger question is why do you need to do this?
for example, if you have 4gb of memory, how much actual memory is given to applications, can you configure this.
No, this isn't a configurable value. When a .NET application starts up the operating system allocates a block of memory for it to use. This is handled by the OS and there is no way to configure the algorithms used to determine the amount of memory to allocate. Likewise, there is no way to configure how much of that memory the .NET runtime uses for the managed heap, stack, large object heap, etc.
I think I read the question a little differently, so hopefully this response isn't too off topic!
You can get a good overview of how much memory your application is consuming by using Windows Task Manager, or even better, Sysinternals Process Monitor. This is a quick way to review your processes at their peaks to see how they are behaving.
Out of the box, an x86 process will only be able to address 2GB of RAM. This means any single process on your machine can only consume up to 2GB. In reality, your likely to be able to consume only 1.5-1.8 before getting out of memory exceptions.
How much RAM your copy of Windows can actually address will depend on the Windows version and cpu architecture.
Using your example of 4GB RAM, the OS is going to give your applications up to 2GB of RAM to play in (which all processes share) and it will reserve 2GB for itself.
Depending on the operating system your running, you can tweak this, using the /3GB switch in the boot.ini, will adjust that ratio to 3GB for applications and 1GB for the OS. This has some impact to the OS, so I'd review that impact first and see if you can live with tradeoff (YMMV).
For a single application to be able to address greater than /3GB, your going to need to set a particular bit in the PE image header. This question/answer has good info on this subject already.
The game changes under x64 architecture. :)
Some good reference information:
Memory Limits for Windows Releases
Virtual Address Space
I think you can use WMI to get all that information
If you don't wish to use WMI, you could use GlobalMemoryStatusEx():
Function Call:
http://www.pinvoke.net/default.aspx/kernel32/GlobalMemoryStatusEx.html
Return Data:
http://www.pinvoke.net/default.aspx/Structures/MEMORYSTATUSEX.html
MemoryLoad will give you a number between 0 and 100 that represents the ~ percentage of physical memory in use and TotalPhys will tell you total total amount of physical memory in bytes.
Memory is tricky because usable memory is a blend of physical (ram) and virtual (page file) types. The specific blend, and what goes where, is determined by the operating system. Luckily, this is somewhat configurable as Windows allows you to stipulate how much virtual memory to use, if any.
Take note that not all of the memory in 32-bit Windows (XP & Vista) is available for use. Windows may report up to 4GB installed but only 3.1-3.2GB is available for actual use by the operating system and applications. This has to do with legacy addressing issues IIRC.
Good Luck
I've written a little application for consuming memory either on disk, or RAM. The reasoning behind this is to test how certain parts of the application behave with small amounts of memory and testing various installers etc. with low disk space. It's quite useful, however currently I've had to limit them to 2Gb.
Unfortunately sometimes I need to consumer more than just 2Gb and have to open the application up several times which is rather annoying. So simply, is there a way I can get around this 2Gb limitation on 32bit OS's?
As far as eating disk space, you can go over the 2GB barrier by creating multiple files, instead of just one. For memory, you might consider having the process automatically spawn enough child processes to consume the amount of RAM you're trying to eat.
For files on disk, you shouldn't be limited to 2GB, what format are the disks using?
FAT = 4GB
NTFS = 16TB
The .NET memory model is subject to the same limits of all applications. Nominally this is 2GB per application on a 32-bit operating system. There are some generic options which may allow you to increase this.
The /3GB switch in the boot.ini increases the 2Gb to 3GB.
PAE (Physical Address Extensions) which allows you to access memory above 4GB in a page-switching method. You would normally need to write support for this yourself (or hope Microsoft have done it for you in the framework/CLR).
See this detailed description of your options (for Windows in general).