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1answer
42 views

Why deleting big files from tmpfs is not instantaneous?

$ cat /proc/mounts | egrep ' /tmp ' tmpfs /tmp tmpfs rw,nosuid,nodev,relatime 0 0 $ dd if=/dev/zero bs=1M count=3000 of=/tmp/q 3000+0 records in 3000+0 records out 3145728000 bytes (3.1 GB) copied, ...
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0answers
11 views

FORTRAN executables: heap maxed out

I am trying to run a FORTRAN program on stampede (xsede machine). The error message I am getting is 'heap maxed out'. I think it has something to do with virtual memory allocation. So I use the ...
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1answer
24 views

Downsides of processes with high virtual size but low RAM and GPU memory use

I have noticed that some of my processes take a lot of virtual size in my computer. I understand that the virtual size of a process is the sum of memory it is actually using, memory it has mapped into ...
3
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1answer
19 views

FDT relocated by U-Boot cannot be accessed by Linux (in highmem)

We run a customized version of U-Boot on an ARM-based embedded system and would like to load Linux 4.3 with a device tree blob. The system features 1GB of RAM of which the top 128MB are reserved for ...
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0answers
31 views

Linux kernel running only with use of physical address

Is theoretically possible to make Linux which for its own kernel (include modules) uses only physical addresses? (it means it completely omits MMU) For processes there would be normal virtual space ...
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1answer
42 views

What is page fault and when does it occur? [closed]

In an interview I was asked this question: what is a page fault and when does it happen?
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2answers
26 views

prevent from writing to a large continuous section of virtual memory [closed]

How can an operating system kernel efficiently prevent a user process from writing to a large continuous section of virtual memory?
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0answers
15 views

How does an OS detect an access to random memory address of a compiled program? [duplicate]

I've read a couple things about memory management/virtual memory and I need a little more details on one important point. If I compile a program and it does an access to a hard-coded address without ...
3
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1answer
196 views

Accessing Memory Mapped I/O is slow

I have a Terasic-SoCKIT(fpga & arm cortex a9) and I have Linux running on the HPS. I'm trying to access the memory mapped I/O, wrote a simple character driver with functions "request_mem_region" ...
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0answers
11 views

How do I find corresponding kernel virtual addresses and userspace virtual addresses for a coreboot table driver?

How does kernel virtual addresses relate to userspace virtual addresses and is there a way to map the two with a kernel function? Some background: Coreboot puts some information in a table structure ...
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0answers
46 views

What does it mean when a private VM page is none of `rwx`?

UPDATE: It's a padding: every such non-rwx area is preceded with a readable and/or writable area and together they constitute a 64Mb segment (for 64bit architecture). A relevant question on SO: ...
7
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1answer
556 views

How do I increase the maximum swap space on Mac OS X?

On Mac OS X Yosemite 10.10.5, when I try to run a calculation that needs to allocate and use 128 GB of memory (it is a command line program written in C), the kernel kills my process with extreme ...
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0answers
50 views

Where can I find the MMU,CR3 and TLB for creating virtual addresses?

I want to understand virtual addressing and read many times the terms: MMU TLB (Translation Lookaside Buffer) and CR3 But currently I'm a bit confused. My confusion is: MMUThe MMU is hardware. ...
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0answers
48 views

When waiting on a pagefault, in what kind of sleep is a task?

Are tasks put into interruptible/uninterruptible/killable sleep when waiting on a pagefault? Does it matter, what kind of pagefault is it?
2
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2answers
65 views

Shared library load mem address region is architecture dependent?

I see that on x86, in a process's VM, shared libraries are loaded between heap and stack, i.e. the mmap area as noted in most of the online articles. But on a PowerPC linux box, I see that all ...
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2answers
108 views

On page fault, how does Unix determine if the faulting address is in swap space?

When a page fault occurs for a virtual address for any process how does the linux/unix operating system determine whether that page (of that virtual address) was swapped previously present in memory ...
4
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1answer
158 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 ...
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0answers
36 views

Print kernel memory layout

Userland memory layout can be inspected by looking into /proc/self/maps. I am wondering if there is a similar facility allowing to inspect runtime kernel memory layout?
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2answers
227 views

Physical Address Extension - how do virtual addresses work?

I'm running Debian Linux. uname -m says i686 which means 32-bit architecture machine with pae flag enabled. getconf LONG_BIT is 32. Installed RAM capacity is 6GB. My /proc/cpuinfo has an entry ...
3
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1answer
220 views

Kernel address space layout

Userland address space is well documented, which includes segments like heap, stack, .text, .bss, etc. But there is not enough documentation on kernel address space. Since certain virtual address is ...
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0answers
49 views

Why process is killed while a lot of memory is free?

I am running a python script in ipython. This script will take about 8GB RAM. The system has more than 80 GB free RAM but the swap is nearly 0. My script was killed after it runned for a while. I want ...
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0answers
85 views

How do I vmtouch a directory (not the files it contains)?

The vmtouch(8) tool allows locking a file or files in memory. It has recursive mode, but the directories are used just for discovering files and are not locked themselves. How do I lock a directory ...
1
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1answer
104 views

Why does my process take too long to die?

Basically I'm using Linux 2.6.34 on PowerPC (Freescale e500mc). I have a process (a kind of Virtual Machine that was developed in-house) that uses about 2.25 G of mlocked VM. When I kill it, I notice ...
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0answers
81 views

Is High Virtual Memory usage a problem or may cause problems?

In our server, we have a python based code that listen ports. The amount of Virtual Memory it uses is increased greatly with time Like: USER PID %CPU %MEM VSZ RSS TTY STAT ...
3
votes
1answer
108 views

How do I forbid access to physical memory in Linux?

I'm on an embedded system (Zynq from Xilinx. It uses ARMv7, Cortex-A9), and running Linux. I need to ensure that no access to a certain physical memory range is ever made, either accidentally by the ...
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0answers
26 views

Page Fault Frequency Algorithm - Compute number of frames and mean resident set

I'm reading about Page Fault Frequency algorithm but I don't understand how can I compute the number of frames. For example I have my reference string: 112233444412412214432255543 and control ...
1
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1answer
83 views

Case study of virtual memory management

Need help in understanding virtual memory concept. When a process requesting for 2GB mapping onto the virutal memory in Linux environment of 4GB ( 1GB Kernel : 3GB Userspace), when already another ...
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0answers
41 views

fast way to find the address range from the given info

I have a question, If I am given some memory devices with size specifications, how do i map it to address range quickly. if the address space is of 32 GB. Ex: ROM - 1Mb 3 RAMs - 2 GB each 2 FLASH - ...
1
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1answer
202 views

Is the Linux kernel affected by paging?

Is the whole kernel always loaded to RAM whatever the size of the RAM? In other words, can the Linux kernel be affected by paging (some part of kernel reside in virtual memory)?
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2answers
99 views

How to get the virtual storage size of a process continuously?

We all know that top command monitors the running processes continuously. I have an application that is running continuously in an embedded Linux and I need to monitor its VSZ (Virtual storage size) ...
0
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1answer
99 views

/dev/mapper/vg00-var maxing out

Over the past few years we have had multiple Linux servers have the same problem time and time again: our /dev/mapper/vg00-var folder maxes out at 100%, which means all sites on the server die. We ...
10
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1answer
223 views

Does anyone actually use and benefit from transparent huge pages?

I've been struggling with transparent huge pages performance issues of late, and noticed many database systems recommend turning it off. I am talking Oracle, Postgresql, MySQL, Cassandra, NuoDB, ...
2
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0answers
68 views

JVM low-memory tuning

What command-line options would provide the lowest memory-footprint JVM, in OpenJDK, or possibly other JVMs (Linux/Debian)? I'm willing to disable JIT, live with slow or choppy garbage collection, ...
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0answers
58 views

In the Linux Kernel what file/process controls the assignment of permissions to memory pages?

A given memory page may be writable, readable or executable. What kernal source code file in the linux kernal describes the setting of these rights? What process or kernal data structure would set the ...
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2answers
454 views

Generate major page faults

Is it possible to generate major page faults in the linux kernel at will? Can a program be written such that it is guaranteed to cause a major page fault on it's execution.
1
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1answer
109 views

Linux always hangs when out of physical memory

I'm using ArchLinux, with 3.18.6-1 kernel, when a software uses more than physical memory (when total memory used is >5.8 GB), it always lags, unresponsive, and all that I can do is reset the ...
2
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0answers
77 views

How can I let high priority processes continue when low priority processes are causing free memory to be low

Ok I'm not sure if this is the correct place to post this. It is more of a 'why not' question than a 'how to' one (assumption is that it isn't/can't be done). Why don't we allow RAM to be partitioned ...
0
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2answers
119 views

Are the size of a memory page and the size of a file system cluster always the same?

From http://en.wikipedia.org/wiki/Page_%28computer_memory%29 A page, memory page, or virtual page is a fixed-length contiguous block of virtual memory, described by a single entry in the page ...
5
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1answer
307 views

When does swap start to be used? When does a process get an out of memory error and be killed?

When does swap start to be used? Is it when the memory is fully used? Or when the memory hasn't been fully used? When does a process get an "Out of memory" error and be killed by the kernel? is it ...
3
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0answers
299 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 ...
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0answers
488 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 ...
0
votes
1answer
145 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
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0answers
710 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 ...
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3answers
14k 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
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1answer
114 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
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1answer
503 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 ...
1
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1answer
304 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 ...
1
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1answer
84 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
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1answer
116 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 ...
2
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0answers
132 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 ...