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Questions tagged [memory]

In computing, memory refers to the state information of a computing system, as it is kept active in some physical structure.

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149
votes
4answers
131k views

How do I read from /proc/$pid/mem under Linux?

The Linux proc(5) man page tells me that /proc/$pid/mem “can be used to access the pages of a process's memory”. But a straightforward attempt to use it only gives me $ cat /proc/$$/mem /proc/self/...
188
votes
8answers
260k views

Limit memory usage for a single Linux process

I'm running pdftoppm to convert a user-provided PDF into a 300DPI image. This works great, except if the user provides an PDF with a very large page size. pdftoppm will allocate enough memory to ...
12
votes
2answers
10k views

How can I get the amount of available memory portably across distributions?

The standard files/tools that report memory seem to have different formats on different Linux distributions. For example, on Arch and Ubuntu. Arch $ free total used free ...
15
votes
2answers
14k views

real memory usage

if I understand correctly, in the following output produced by free, 3535m is the actual free memory available to applications, only 413m is used, is this correct? need some clarification on the ...
68
votes
9answers
144k views

Correctly determining memory usage in Linux

I'm a bit confused on some of the results I am seeing from ps and free. On my server, this is the result of free -m [root@server ~]# free -m total used free shared ...
46
votes
6answers
5k views

How do I use swap space for emergencies only?

I have a Debian (Buster) laptop with 8 GB RAM and 16GB swap. I'm running a very long running task. This means my laptop has been left on for the past six days while it churns through. While doing ...
47
votes
5answers
30k views

Measuring RAM usage of a program

time is a brilliant command if you want to figure out how much CPU time a given command takes. I am looking for something similar that can measure the max RAM usage of the program and any children. ...
113
votes
1answer
119k views

How does the OOM killer decide which process to kill first?

This answer explains the actions taken by the kernel when an OOM situation is encountered based on the value of sysctl vm.overcommit_memory. When overcommit_memory is set to 0 or 1, overcommit is ...
44
votes
4answers
40k views

grep: memory exhausted

I was doing a very simple search: grep -R Milledgeville ~/Documents And after some time this error appeared: grep: memory exhausted How can I avoid this? I have 10GB of RAM on my system and few ...
97
votes
13answers
53k views

Do I need swap space if I have more than enough amount of RAM?

From what I understand, the purpose of a swap partition in Linux is to free up some "not as frequently accessed" information from RAM and move it to a specific partition on your harddrive (at the cost ...
25
votes
3answers
112k views

Actual memory usage of a process

The following are the memory usage of mysql and apache respectively on my server. As per the output of pmap say, mysql is using about 379M and apache is using 277M. [root@server ~]# pmap 10436 | ...
15
votes
2answers
6k views

30% of RAM is “buffers”. What is it?

How can I describe or explain "buffers" in the output of free? $ free -h total used free shared buff/cache available Mem: 501M 146M ...
2
votes
1answer
2k views

Why does swappiness not work?

We have a RHEL 7 machine, with only 2G of available RAM: free -g total used free shared buff/cache available Mem: 31 28 0 ...
30
votes
2answers
30k views

How to blacklist a correct bad RAM sector according to MemTest86+ error indication?

MemTest86+ (the version included with Ubuntu 13.04) says Failing address: 002f796c48 - 759.5 MB What should I specify in the memmap kernel parameter to bypass this area? I've tried running ...
49
votes
3answers
75k views

How to create a user with limited RAM usage?

So I have 4 GB RAM + 4GB swap. I want to create a user with limited ram and swap: 3 GB RAM and 1 GB swap. Is such thing possible? Is it possible to start applications with limited RAM and swap ...
21
votes
4answers
17k views

How to re-load all running applications from swap space into RAM?

If my desktop run out of memory and swaps a lot then I free or kill the application wasting my RAM. But, after that, all my desktop/applications have been swapped and are horribly slow, do you know a ...
15
votes
1answer
6k views

Turning off swapping for only one process with cgroups?

I would like to turn off swapping for only one process. Swap should work as usual for the other processes. How I can implement this with cgroups?
5
votes
2answers
4k views

`free`: output format

I use free to get the amount of free space on some of my servers. Its output is something like: $ free -m total used free shared buffers cached Mem: 374 ...
2
votes
2answers
673 views

Can I see the amount of memory which is allocated as GEM buffers?

My /proc/meminfo shows about 500 MB is allocated as Shmem. I want to get more specific figures. I found an explanation here: https://lists.kernelnewbies.org/pipermail/kernelnewbies/2013-July/008628....
221
votes
8answers
288k views

How to display meminfo in megabytes in top?

Sometimes it is not comfortable to see meminfo in kilobytes when you have several gigs of RAM. In Linux, it looks like: And here is how it looks in Mac OS X: Is there a way to display meminfo in ...
48
votes
3answers
65k views

What do the “buff/cache” and “avail mem” fields in top mean?

Within the output of top, there are two fields, marked "buff/cache" and "avail Mem" in the memory and swap usage lines: What do these two fields mean? I've tried Googling them, but the results only ...
15
votes
2answers
4k views

What's the use of having a kernel part in the virtual memory space of Linux processes?

I found a similar question but still it doesn't answer my questions Do the virtual address spaces of all the processes have the same content in their "Kernel" parts? First off, considering ...
6
votes
1answer
1k views

How large are the “watermark” memory reservations on my system?

swappiness This control is used to define how aggressive the kernel will swap memory pages. Higher values will increase aggressiveness, lower values decrease the amount of swap. A value of ...
72
votes
2answers
38k views

Will Linux start killing my processes without asking me if memory gets short?

I was running a shell script with commands to run several memory-intensive programs (2-5 GB) back-to-back. When I went back to check on the progress of my script I was surprised to discover that some ...
37
votes
3answers
11k views

What does the vm.swappiness parameter really control?

Per the kernel documentation: This control is used to define how aggressive the kernel will swap memory pages. Higher values will increase aggressiveness, lower values decrease the amount of swap. ...
26
votes
4answers
42k views

How can I reserve a block of memory from the Linux kernel?

I have a device that needs a block of memory that is reserved solely for it, without the OS intervening. Is there any way to tell BIOS or the OS that a block of memory is reserved, and it must not ...
16
votes
3answers
9k views

On system memory… specifically the difference between `tmpfs,` `shm,` and `hugepages…`

I've been curious lately about the various Linux kernel memory based filesystems. Note: As far as I'm concerned, the questions below should be considered more or less optional when compared with a ...
20
votes
6answers
24k views

Is there a tool that allows logging of memory usage?

I want to monitor memory usage of a process, and I want this data to be logged. Does such a tool exist?
11
votes
1answer
10k views

Why does Linux show both more and less memory than I physically have installed?

I know about swap - this question isn't about that. In dmesg, the Linux (x86-64) kernel tells me this about how much memory I have: [ 0.000000] Memory: 3890880k/4915200k available (6073k kernel ...
12
votes
2answers
1k views

Does Linux perform “opportunistic swapping”, or is it a myth?

Suppose a program asks for some memory, but there is not enough free memory left. There are several different ways Linux could respond. One response is to select some other used memory, which has ...
4
votes
3answers
9k views

What is the buffers column in the output from free?

These questions briefly list the format of the free command, noting that buffers is kernel memory that must be written out to disk and cache is file data that does not need to be written disk. On my ...
454
votes
9answers
680k views

How to display `top` results sorted by memory usage in real time?

How can I display the top results in my terminal in real time so that the list is sorted by memory usage?
189
votes
14answers
177k views

How to fill 90% of the free memory?

I want to do some low-resources testing and for that I need to have 90% of the free memory full. How can I do this on a *nix system?
104
votes
7answers
96k views

What are high memory and low memory on Linux?

I'm interested in the difference between Highmem and Lowmem: Why is there such a differentiation? What do we gain by doing so? What features does each have?
51
votes
1answer
59k views

Getting information about a process' memory usage from /proc/pid/smaps

For a given process in /proc/<pid>/smaps, for a given mapping entry what are: Shared_Clean Shared_Dirty Private_Clean Private_Dirty Is Shared_Clean + Shared_Dirty the amount of memory that is ...
67
votes
2answers
77k views

Need explanation on Resident Set Size/Virtual Size

I found that pidstat would be a good tool to monitor processes. I want to calculate the average memory usage of a particular process. Here is some example output: 02:34:36 PM PID minflt/s ...
45
votes
1answer
29k views

Loading of shared libraries and RAM usage

I'm wondering about the way Linux manages shared libraries. (actually I'm talking about Maemo Fremantle, a Debian-based distro released in 2009 running on 256MB RAM). Let's assume we have two ...
20
votes
1answer
15k views

What does the Virtual kernel Memory Layout in dmesg imply?

While going through the "Output of dmesg" I could see a list of values which i am not able to understand properly. Memory: 2047804k/2086248k available (3179k kernel code, 37232k reserved, 1935k ...
27
votes
2answers
7k views

Is it possible to trigger OOM-killer on forced swapping?

Is it possible to have the system preemptively swap out inactive pages (vm.swappiness), but invoke the oom-killer when the system runs out of RAM (as opposed to running out of memory) and is forced to ...
39
votes
4answers
28k views

System hanging when it runs out of memory

I've got an eeePC 900a: it has a 8GB flash as disk and only 1GB of RAM. The Linux distribution installed on it is ArchLinux. When the system runs out of memory it becomes extremely unresponsive: it ...
10
votes
1answer
10k views

What page replacement algorithms are used in Linux kernel for OS file cache?

Linux uses the unused portions of memory for file caching, and it cleans up the space when needed. My question is about how it picks a victim page for replacement? There are various algorithms (LRU, ...
39
votes
7answers
47k views

Is there a way to limit the amount of memory a particular process can use in Unix? [duplicate]

I need to test a process for memory management. I do not have the source, so I need to do all the testing from the OS side. I want to be able to say something like limitmemory 400k -p <pid> Is ...
9
votes
2answers
11k views

MMU-less kernel?

I would like to try compile mmu-less kernel. From what I found in configuration there is no option for such a thing. Is it possible to be done?
8
votes
2answers
16k views

Out of swap - what happens?

On my Debian VM machine with 512 MB RAM and 348 MB swap, what will happen if I open a 1 GB file in an editor and get out of memory? Will it crash the system? Or if not, how will Linux handle ...
8
votes
1answer
6k views

Shared library mappings in /proc/pid/maps

Why does /proc/pid/maps contain a few records for the same library ? Here is an example: 7fae7db9f000-7fae7dc8f000 r-xp 00000000 08:05 536861 /usr/lib/x86_64-linux-gnu/libstdc++....
8
votes
1answer
8k views

Does kernel: EDAC MC0: UE page 0x0 point to bad memory, a driver, or something else?

kernel: EDAC MC0: UE page 0x0, offset 0x0, grain 0, row 7, labels ":": i3200 UE All of a sudden today, our CentOS release 6.4 (Final) system started throwing EDAC errors. I rebooted, and the errors ...
7
votes
1answer
6k views

what does mean by HardwareCorrupted, DirectMap4k, DirectMap2M fields in “/proc/meminfo” file of Linux?

I am looking for description of following terms: HardwareCorrupted, DirectMap4k, DirectMap2M fields in "/proc/meminfo" file of Linux. I could find the following description for the fields ...
5
votes
1answer
2k views

Tracking huge buffer usage under Linux

I have a Linux server running under Debian Lenny with 4Go of RAM. It doesn't run much, just: Postfix/spamassassin (daemon mode) Bind9 KVM (one guest - 1Go of RAM for it) Every day at exactly 3:05 ...
2
votes
1answer
498 views

atop shows `swout` (swapping) when I have gigabytes of free memory. Why?

Why did atop show that I was swapping out over 20,000 pages - over 80 megabytes - when I had gigabytes of free memory? I have not noticed a performance problem with this. I simply wish to take the ...
1
vote
2answers
6k views

free / top difference. Does free show virtual memory?

free -m shows me the following in my system: total used free shared buffers cached Mem: 3954 3842 111 0 248 2585 -/+ ...