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4
votes
1answer
352 views

Spike in swap utilisation without high swap rate

Every Saturday, for reasons unknown to me, one of my servers experiences a spike in swap utilisation. It's not necessarily a problem as there is plenty of free memory available, but I'd still like to ...
1
vote
1answer
355 views

Clear Memory Cache on Amazon EC2

In our project we have a few tests which run for about 3-4 hours continuously. In due course, the tests fail as they couldn't find enough memory. On googling, I found that running the following ...
2
votes
3answers
957 views

Linux / JVM - OutOfMemoryError: unable to create new native thread

I have a memory problem with a Linux server (CentOS). It is a VM. Below is the context. It has 70Gb of RAM. There are 2 tomcat running on it. One tomcat is given a heap of 13Gb and the other one a ...
3
votes
0answers
17 views

Why does saving a KVM-QEMU VM requires additional memory?

I have three VMs running on Red Hat Enterprise Linux with 8 GB RAM, each of the VMs has 3 GB allocated, and I also run a 512 MB VM. If we also consider the guest OS's memory usage (usually 1.5 GB due ...
1
vote
0answers
80 views

Xorg consuming 1.1GB, is it a leak?

I am facing a problem wherein Xorg starts to consume more and more memory and finally eats up the whole swap space. As shown below, Xorg's virtual memory is about 1.1GB. My system runs only one GTK ...
1
vote
1answer
561 views

Iotop shows swapin but vmstat si is zero

I run iotop and vmstat on a CentOS server. Under some load the iotop swapin column starts to display values around 5% to 20% for some processes. But vmstat si an so remain zero. I thought that vmstat ...
0
votes
1answer
48 views

What is the difference between MAC OS X “Virtual Memory” and Linux/Unix Swap? [duplicate]

I would like to understand the difference of MAC OS X "Virtual Memory" and Linux/Unix Swap. I ask this because I observed that MAC OS X "Virtual Memory" seems to work way more efficient (in desktop ...
1
vote
2answers
1k views

Discrepancy between reported used memory and sum of application memory usage

I'm running a desktop system that quite regularly suffers from lack of memory, this prompted me to investigate what causes the issue in the first place. Problem is, there's no single process that ...
1
vote
0answers
39 views

About mem and vmem

I am working with a cluster machine running under linux. I have a shell script that uses mpirun to submit my jobs to the cluster machine. In that same script, I can choose the number of nodes that ...
1
vote
3answers
108 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 | ...
1
vote
1answer
39 views

A simple definition for Virtual Memory

How correct is this picture that I drew up if I am to explain Virtual Memory to some of my colleagues? There are hundreds of documents available online explaining virtual memory, but I am yet to ...
0
votes
1answer
62 views

Opening files of size larger than RAM, no swap used.

I found myself asking this question while doing small experiments and reading upon how memory is managed in Linux. I have a 64-bit Centos 6.5 machine with 512M RAM and 1G SWAP. I created a 1GB file ...
0
votes
0answers
36 views

AIX Memory Limits

I cannot find these numbers anywhere on the IBM Web site or even random blogs that Google finds. Questions What is the maximum physical memory size a POWER7 CPU supports? What is the maximum ...
0
votes
2answers
221 views

Is Inactive memory related to the Commited but unused?

From the Linux procfs documentation: Active: Memory that has been used more recently and usually not reclaimed unless absolutely necessary. Inactive: Memory which has been ...
0
votes
0answers
18 views

«nm» shows zero VMA: where is the symbol will be mapped?

I am look at the functions of my compiled application via «nm» — I need to find an address to set a breakpoint to the «send()» function. The problem is that this function accordingly to «nm»'s output ...
1
vote
1answer
42 views

benefits of huge pages on a laptop/desktop

I have read about huge pages and its the (potential) benefits. However, I am still confused whether this is mostly beneficial on a server with lots of RAM, or if it can be advantageous on a ...
1
vote
3answers
563 views

Viewing virtual memory usage

I started 700+ threads from a single program And my /proc/[PID]/status file shows the following output. VmPeak: 7228104 kB VmSize: 7228104 kB VmLck: 0 kB VmHWM: 3456 kB VmRSS: ...
2
votes
0answers
67 views

Disk page cache size in Linux for integrity purposes

I am trying to bound corruption in a block-based disk format in the presence of plausible machine failures in a Linux-specific application. That is, the file is read and written in application-defined ...
28
votes
2answers
1k views

Why did powering down my machine after a bad `rm` save my files?

Classical situation: I ran a bad rm and realized immediately afterwards that I had removed the wrong files. (Nothing critical and I had tolerably recent backups, but still annoying.) Knowing that ...
0
votes
0answers
28 views

How fast is a process reading/writting virtual memory?

So, we have top, htop, iotop, iostat, vmstat, etc, to measure many different things on Linux, but how can one measure how much MB/s a process is reading and writting to/from RAM, i.e., virtual memory? ...
0
votes
1answer
38 views

to print address space of a process in ubuntu 12.04

How do I print an address space of a process by taking the process' PID?
1
vote
1answer
62 views

How logical address of one process differs from the logical address of another?

I am a newbie. I am reading Understanding Linux Kernel. There, I am trying to understand how logical address got translated to physical address. To my understanding, I believe logical address got ...
1
vote
1answer
76 views

Malloc and Paging

When a user process invokes malloc(n), are there any physical pages allocated to the process? I believe No since malloc allocates from the heap. Is this correct?
2
votes
1answer
160 views

Is a page contiguous in the virtual address space or physical memory or both?

Wikipedia says that: A page, memory page, or virtual page is a fixed-length contiguous block of virtual memory, described by a single entry in the page table. It is the smallest unit of data ...
2
votes
4answers
577 views

How much RAM needed for preventing use swap?

At my system always available some "Free" and "Inactive" memory, but sometimes system move couple megabytes to swap. Per night it maybe around 100MB, but for a few days in swap could be more than ...
6
votes
2answers
679 views

How does stack allocation work in Linux?

Does the OS reserve the fixed amount of valid virtual space for stack or something else? Am I able to produce a stack overflow just by using big local variables? I've wrote a small C program to test ...
7
votes
3answers
4k views

Why is the theoretical RAM limit for RHEL 6 128 TB and how is this determined?

I'm studying for RHCSA and am confused by a statement I came across in some training material: There is no practical maximum RAM, as theoretically, you could run 128 TB of RAM on RHEL 6. But ...
2
votes
0answers
105 views

Virtual kernel memory layout in dmesg linux kernel 2.6.31

I'm working on a embedded linux project for ARM architecture, kernel version is 2.6.31.12-rt21. In dmesg, I cannot see the virtual kernel memory layout like this: virtual kernel memory layout: ...
1
vote
1answer
1k views

Drop_caches doesn't drop caches?

Sometimes I see my swap file is a bit bigger then usual. I tried sync && echo 3 > /proc/sys/vm/drop_caches to no avail. But when I tried swapoff -a it takes a bit longer but the swap file ...
3
votes
0answers
629 views

How extended (4MB) and regular (4KB) paging coexist?

On x86 architecture, "Extended paging" allows page frames (physical memory) to be 4 MB instead of 4 KB. The book "Understanding the Linux Kernel, 3rd" at chapter 2 "Memory Addressing", sub-chapter ...
6
votes
1answer
2k views

The meaning of output of pmap

I wrote main.c in Linux: int main() { while (1){} } When I compile and start it, I can pmap it: # pmap 28578 28578: ./a.out 0000000000400000 4K r-x-- /root/a.out 0000000000600000 4K ...
5
votes
2answers
168 views

1GB huge page - Is writing occurring in 1GB chunks?

I'm trying to understand the relation between huge page size and how data is actually being written to RAM. What happens when a process uses a 1GB huge page - does writing occur in 1GB chunks? I ...
6
votes
3answers
2k views

How to set up properly zram and swap

I'm configuring & compiling new 3.0 kernel. One of the goodies I planned to use for some time (by patching) that was merged into 3.0 is zram. Is it possible to set both hdd swap and zram swap so ...
4
votes
1answer
51 views

Memory consumption of a script

Is there way to check the memory (physical & virtual) consumption of a script, of course in the moment of its execution. Calculating the used memory minus the used memory before and after the ...
0
votes
0answers
16 views

VMap Fedora 12 equivalent

I'd like to see how Fedora manages the Virtual Memory. I was used to VMap on Windows, however I can't find anything to download on Fedora 12 that could fit my needs. I can't find something like ...
3
votes
1answer
41 views

program executing for 2 days

I have a java program which implements the Hungarian algorithm. I made changes to the existing code in such a way that the input is read from file. I have a pretty huge input around 32,000 rows for ...
2
votes
2answers
184 views

Is there a good benchmark for virtual memory performance?

Aside from running memory benchmarks, has anyone used a benchmark that stresses the virtual memory subsystem? I'm curious to see how performance differs in virtual machines with and without EPT ...
1
vote
1answer
672 views

Do VmPeak & VmHWM have any measurement periods?

While reading kernel documentation I came across VmPeak & VmHWM, and it's a bit unclear to me. VmPeak in /proc/<pid>/status is described to be peak virtual memory size. Peak for what ...
0
votes
1answer
756 views

How to find the page size, associativity, and TLB size and number of entries?

Under an Ubuntu system, are there commands for looking up: the page size, n in n-way cache associativity, TLB cache's size and number of entries?
1
vote
2answers
286 views

TLB cache flusing when a page is swapped out

I recently heard that Linux simply flushes the TLB cache when the corresponding data in that physical address is swapped out, resulting in underutilization of the TLB. I don't know whether all OSes do ...
19
votes
1answer
14k 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 ...
0
votes
1answer
288 views

Reading virtual memory

Is it possible to read virtual memory even if /dev/kmem is not available? I know that I can recompile kernel to allow this file, but that's not the solution I'm looking for. Is there some tricky way I ...
2
votes
3answers
479 views

How can I find the amount of memory consumed by a process?

How can I find the amount of main memory consumed by a process using ps aux? I have a process which runs for half an hour. Is it possible to find the maximum amount of main memory consumed by it ...
8
votes
1answer
2k views

Zswap, Zram, Zcache desktop usage scenarios

I've been trying to understand the difference in use cases for Zswap, Zram, and Zcache. Apologies in advance for the long/slightly sloppily worded question. I've done a bunch of googling, and I ...
9
votes
1answer
4k views

Unable to handle kernel paging request?

[Disclaimer: I was initially a little nervous about posting this here, so I asked on Meta if discussing homebrew / modding was acceptable. Based on the response I've gotten from several veteran ...
1
vote
1answer
134 views

How does the kernel know how much user addressable memory to set aside?

I was reading up on a rather-dated article on the kernel managing memory and had this question on where the Page Table Entries (PTE) would go into. For this example, the author assumes we are on a ...
3
votes
0answers
153 views

GNU/Linux swapping blocks system

I have used GNU/Linux on systems from 4 MB RAM to 512 GB RAM. When they start swapping, most of the time you can still log in and kill off the offending process - you just have to be 100-1000 times ...
5
votes
1answer
93 views

kernel address space mappings with respect to virtual address space - a question based on text by Robert Love

In LKD 3rd edition, chapter 12 under Zones, Robert Love says: In particular, Linux has to deal with two shortcomings of hardware with respect to memory addressing: Some hardware devices ...
10
votes
6answers
2k views

Can Linux “run out of RAM”?

I saw several posts around the web of people apparently complaining about a hosted VPS unexpectedly killing processes because they used too much RAM. How is this possible? I thought all modern OS' ...
0
votes
2answers
360 views

Linux kernel with absolutely no virtual memory [duplicate]

I am interested in obtaining (or building myself) a version of the Linux kernel that has absolutely no virtual memory and none of its attendant overhead. No swap file, no nothing. What are my ...