Clear Memory of Residual Applications no longer Running

johnmccarthy · 11-08-2011, 06:48 AM

Our RHEL 5 systems run an application that absorbs much of the memory and processors power. When the application ends the our RHEL 5 systems still run slow. The command top does not reflect the application is running any longer so we are forced to reboot to clear the buffer. Is there anyway to clear or flush the memory without rebooting the computer? A million thanks,

Johnny Mac

tronayne · 11-08-2011, 07:11 AM

Yes, there is -- simply

Code:

sync;sync;sync

You do it three times to make sure that everything is flushed; the first will take a while, the second significantly less time and the third instantly.

If this is an application you've written, be sure to close all open files in the application and exit cleanly; e.g., in C

Code:

fclose (file1);
fclols (file2);
exit (0);

Using sync from the command line is also not a bad idea if you're writing to a flash drive; they're not anywhere near as fast as disk drives and, sometimes, the write buffers are not flushed as quickly as you'd think so just entering sync on a command line will "make sure."

Hope this helps some.

Juako · 11-08-2011, 07:14 AM

AFAICT as long as the process is really finished, its memory will be eventually reclaimed by applications or the buffer cache.

johnsfine · 11-08-2011, 08:18 AM

Quote:

Originally Posted by johnmccarthy

When the application ends the our RHEL 5 systems still run slow.

I doubt any real slow down lasts a significant time after the application ends.

I'm pretty sure you are misunderstanding memory statistics (seeing memory filled by buffers and cache) and expecting that to cause a slow down, and imagining the slow down you expect.

It is perfectly normal for buffers and cache to be filled up by some large applications. While there are ways to free that memory, freeing that memory will not improve system performance.

If you had interactive processes paused during the run of the big application, those will be slow to regain their memory after the big application ends. But they will be no faster (maybe even a little slower) at regaining their memory if you clear the cache at the end of running the big application.

Some commonly used applications might typically launch fast because their code is usually in cache. Running the big application might push those out of cache, so they launch slowly the next time they are run. Again, flushing cache after running the big application will not help (and might hurt).