Resource Limits on the Linux Clients - Revision history

Steve410: /* Memory Usage */

2024-11-08T15:07:14Z

Memory Usage

Phil: /* Number of Processes */

2024-05-15T18:26:31Z

Number of Processes

Phil: /* Memory Usage */ memory limit now only applies to compute systems

2024-05-15T18:17:41Z

Memory Usage: memory limit now only applies to compute systems

Phil: /* Memory Usage */

2024-03-14T13:09:29Z

Memory Usage

Phil: /* Number of Processes */

2024-03-14T13:05:46Z

Number of Processes

Phil: /* Number of Processes */

2024-03-14T13:04:17Z

Number of Processes

Phil: /* Memory Usage */

2023-08-22T15:34:46Z

Memory Usage

Phil at 14:12, 24 April 2023

2023-04-24T14:12:42Z

Steve410: /* Maximum Process Runtime */

2023-04-20T21:12:24Z

Maximum Process Runtime

Steve410: /* Maximum Process Runtime */

2023-04-20T21:11:10Z

Maximum Process Runtime

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 == Memory Usage ==
-The maximum memory (RAM) usage for a program is '''16 GiB'''.  This limit applies only to the non-lab systems like ugradx and ugradz.  The lab systems (ugrad1 through ugrad24) have no imposed limit, so it's possible for a buggy program to use up all of a system's RAM.  If one lab computer is unresponsive, you can simply use a different one until we're able to fix the problem.
+The maximum memory (RAM) usage for a program is '''16 GiB'''.  This limit applies only to the non-lab systems like ugradx and ugradz.  The lab systems (ugrad1 through ugrad24) have no imposed limit, so it's possible for a buggy program to use up all of a system's RAM.  If one lab computer is unresponsive, you can simply use a different one until we're able to fix the problem.  (But, email [mailto:support@cs.jhu.edu support@cs.jhu.edu] to let us know you experienced an issue, and include the system name as well.)
 Note that this limit applies collectively to every program started from the ''same'' login session.  Running one program that uses 16 GiB of RAM will hit the limit, but so will running eight programs that each use 2 GiB of RAM.

@@ Line 19: / Line 19: @@
 Note that this limit applies to ''threads'', not just processes.  Every process has at least one thread, but many processes run using more than one thread.  You can see a list of all of your processes from the command line by running <kbd>ps x</kbd> .  You can see a list of all your process threads by running <kbd>ps x -L</kbd> .
-If the total number of running processes started from the same login session is at the limit, attempts to start any additional processes will fail.  How that failure is manifested will depend on the program that tried to launch the additional process.  In C, <code>fork()</code> will return -1 and <code>errno</code> will be set to <code>EAGAIN</code>.  A shell will typically give a message along the lines of "fork failed: Resource temporarily unavailable".  In Python, you will typically get a <code>BlockingIOError</code> with a message of "[Errno 11] Resource temporarily unavailable".  The Java exception raised will vary depending on the function having been called; for instance, <code>java.util.concurrent.ForkJoinPool.execute()</code> will raise <code>java.util.concurrent.RejectedExecutionException</code>.
+If the total number of running processes started from the same account is at the limit, attempts to start any additional processes will fail.  How that failure is manifested will depend on the program that tried to launch the additional process.  In C, <code>fork()</code> will return -1 and <code>errno</code> will be set to <code>EAGAIN</code>.  A shell will typically give a message along the lines of "fork failed: Resource temporarily unavailable".  In Python, you will typically get a <code>BlockingIOError</code> with a message of "[Errno 11] Resource temporarily unavailable".  The Java exception raised will vary depending on the function having been called; for instance, <code>java.util.concurrent.ForkJoinPool.execute()</code> will raise <code>java.util.concurrent.RejectedExecutionException</code>.
 == Maximum Process Runtime ==

@@ Line 5: / Line 5: @@
 == Memory Usage ==
-The maximum memory (RAM) usage for a program is '''4 GiB'''.
+The maximum memory (RAM) usage for a program is '''16 GiB'''.  This limit applies only to the non-lab systems like ugradx and ugradz.  The lab systems (ugrad1 through ugrad24) have no imposed limit, so it's possible for a buggy program to use up all of a system's RAM.  If one lab computer is unresponsive, you can simply use a different one until we're able to fix the problem.
-Note that this limit applies collectively to every program started from the ''same'' login session.  Running one program that uses 4 GiB of RAM will hit the limit, but so will running eight programs that each use 512 MiB of RAM.
+Note that this limit applies collectively to every program started from the ''same'' login session.  Running one program that uses 16 GiB of RAM will hit the limit, but so will running eight programs that each use 2 GiB of RAM.
 The limit also applies to memory reservations, whether or not they're actively being used.  This means if you <code>mmap</code> a file, the entire file size will count towards this limit, even though blocks from the file are only paged into RAM on demand.

← Older revision		Revision as of 13:09, 14 March 2024
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	Note that this limit applies collectively to every program started from the ''same'' login session. Running one program that uses 4 GiB of RAM will hit the limit, but so will running eight programs that each use 512 MiB of RAM.		Note that this limit applies collectively to every program started from the ''same'' login session. Running one program that uses 4 GiB of RAM will hit the limit, but so will running eight programs that each use 512 MiB of RAM.
		+
		+	The limit also applies to memory reservations, whether or not they're actively being used. This means if you <code>mmap</code> a file, the entire file size will count towards this limit, even though blocks from the file are only paged into RAM on demand.

	When your program hits the memory limit, any further attempts to allocate memory will fail. How that failure is manifested will depend on your programming language. In C, <code>malloc()</code> (or another memory allocation function) will return <code>NULL</code> and <code>errno</code> will be set to <code>ENOMEM</code>. In Python, a <code>MemoryError</code> exception will be raised. In Java, an <code>OutOfMemoryError</code> will be raised. For other languages, please consult the relevant documentation.		When your program hits the memory limit, any further attempts to allocate memory will fail. How that failure is manifested will depend on your programming language. In C, <code>malloc()</code> (or another memory allocation function) will return <code>NULL</code> and <code>errno</code> will be set to <code>ENOMEM</code>. In Python, a <code>MemoryError</code> exception will be raised. In Java, an <code>OutOfMemoryError</code> will be raised. For other languages, please consult the relevant documentation.

@@ Line 13: / Line 13: @@
 == Number of Processes ==
-We have a limit of '''8192 process threads''' per login session.
+We have a limit of '''8192 process threads''' per account on each of our Linux clients.
 Note that this limit applies to ''threads'', not just processes.  Every process has at least one thread, but many processes run using more than one thread.  You can see a list of all of your processes from the command line by running <kbd>ps x</kbd> .  You can see a list of all your process threads by running <kbd>ps x -L</kbd> .

← Older revision		Revision as of 14:12, 24 April 2023
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	If your disk usage is at its limit, attempts to write additional data to files in the <code>/home</code> filesystem will fail. In C, the <code>write()</code> function will return -1 and <code>errno</code> will be set to <code>EDQUOT</code> (or, in some cases, <code>ENOSPC</code>). Python will raise an <code>OSError</code> exception with message "[Errno 122] Disk quota exceeded". Java ''might not raise an exception'' and instead might just silently fail to write the data.		If your disk usage is at its limit, attempts to write additional data to files in the <code>/home</code> filesystem will fail. In C, the <code>write()</code> function will return -1 and <code>errno</code> will be set to <code>EDQUOT</code> (or, in some cases, <code>ENOSPC</code>). Python will raise an <code>OSError</code> exception with message "[Errno 122] Disk quota exceeded". Java ''might not raise an exception'' and instead might just silently fail to write the data.
		+
		+	[[Category:Linux Clients]]

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 Any program that has consumed more than '''1 week''' of ''accumulated CPU time'' will be terminated.
-"Accumulated CPU time" is the total amount of time spent actively using a single CPU core.  For example, a single-threaded process running continuously for one week will accumulate 1 week of CPU time.  Along the same lines, a process with ''seven'' threads, all running continuously, will accumulate ''seven'' seconds of CPU time for every actual elapsed second and, therefore, will accumulate 1 week of CPU time after running ''for one day''.
+"Accumulated CPU time" is the total amount of time spent actively using a single CPU core.  For example, a ''single''-threaded process running continuously for ''one'' week will accumulate ''one'' week of CPU time.  Along the same lines, a process with ''seven'' threads, all running continuously, will accumulate ''seven'' seconds of CPU time for every actual elapsed second and, therefore, will accumulate ''one'' week of CPU time after running ''for one day''.
 When a program exceeds the CPU time limit, it will be sent the <code>SIGXCPU</code> signal.  If the program has no registered handler for that signal, it will simply stop running and its parent process will be notified.  If it has a registered signal handler, the handler will be given about 30 seconds of runtime to clean up any resources before the process is ended.  The process will be sent a new <code>SIGXCPU</code> signal every second until it exits.  If it's still running after 30 seconds, the process will be forcibly terminated.