How to avoid HDD thrashing

Question

I am developing a large program which uses a lot of memory. The program is quite experimental and I add and remove big chunks of code all the time. Sometimes I will add a routine that is rather too memory hungry and the HDD drive will start thrashing and the program (and the whole system) will slow to a snails pace. It can easily take 5 mins to shut it down!

What I would like is a mechanism for avoiding this scenario. Either a run time procedure or even something to be done before running the program, which can say something like "If you run this program there is a risk of HDD thrashing - aborting now to avoid slowing to a snails pace".

Any ideas?

EDIT: Forgot to mention, my program uses multiple threads.

Answer 1

I'd rather determine reasonable minimum requirements for the computer your program is supposed to run on, and during installation either warn the user if there's not enough memory available, or refuse to install.

Telling him each time he's starting the program is nonsensical.

Answer 2

Windows XP is terrible when there are multiple threads or processes accessing the disk at the same time. This is effectively what you experience when your application begins to swap, as the OS is writing out some pages while reading in others. Windows XP (and Server 2003 for that matter) is utterly trash for this. This is a real shame, as it means that swapping is almost synonymous with thrashing on these systems.

Your options:

• Microsoft fixed this problem in Vista and Server 2008. So stop using a 9 year old OS. :)
• Use unbuffered I/O to read/write data to a file, and implement your own paging inside your application. Implementing your own "swap" like this enables you to avoid thrashing.

See here many more details of this problem: http://stackoverflow.com/questions/9191/how-to-obtain-good-concurrent-read-performance-from-disk

Answer 3

I'm not familiar with Windows programming, but under Unix you can limit the amount of memory that a program can use with setrlimit(). Maybe there is something similar. The goal is to get the program to abort once it uses to much memory, rather than thrashing. The limit would be a bit less than the total physical memory on the machine. I would guess somewhere between 75% and 90%, but some experimentation would be necessary to find the optimal setting.

Answer 4

Chances are your program could use some memory management. While there are a few programs that do need to hold everything in memory at once, odds are good that with a little bit of foresight you might be able to rework your program to reuse or discard a lot of the memory you need.

Your program will run much faster too. If you are using that much memory, then basically all of your built-in first and second level caches are likely overflowing, meaning the CPU is mostly waiting on memory loads instead of processing your code's instructions.

Answer 5

You could consider using SetProcessWorkingSetSize . This would be useful in debugging, because your app will crash with a fatal exception when it runs out of memory instead of dragging your machine into a thrashing situation.

http://msdn.microsoft.com/en-us/library/ms686234%28VS.85%29.aspx

Similar SO question

http://stackoverflow.com/questions/192876/set-windows-process-or-user-memory-limit