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How to Study Effect of zram on Memory Size and Paging?

Situation: to study the effect of zram's virtual memory compression (wiki) on memory's size and its speed Motivation: I experience no effect on the memory's size but increased amount of errors from ...
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0answers
10 views

Why total swaps and page faults/reclaims is empty in ps?

I'm running the following command: sudo ps -axo nswap,majflt,minflt,command | sort -nr | head which suppose to print total swaps in/out, total page faults and reclaims. But for given >400 ...
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1answer
38 views

How to deal with high number of page faults?

I've got ~200000 page faults per second and I think it's a huge number and it affects the overall system performance. I'm using MBP with 16G of RAM. How to deal with such number of page faults (...
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2answers
31 views

When is the page table of a process loaded in memory?

I'd like to know when is the page table of a particular process loaded in main memory by the OS? Is it when the process gets scheduled? Is the OS capable of directly loading the process page table ...
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0answers
30 views

Is there a more efficient way of defragmenting Linux memory other than rebooting?

I am running Gentoo Linux with kernel 4.4.8-hardened-r1, QEMU-KVM version 2.5.1 and 3227 MB of system-visible RAM (without considering RAM taken by BIOS and my AMD APU's graphics). I have a VM that ...
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0answers
36 views

How to convert from virtual address to physical address and back? [migrated]

I'm given a task to write an application that will talk to a device. However this is not a driver since device is still being developed and the application is intended to exercises its first revision. ...
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1answer
28 views

Questions about minor page fault

From Stephen's reply and comment at http://unix.stackexchange.com/a/289446/674 in some cases, data which has been marked for paging out but hasn't yet been paged out. paging out would ...
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1answer
33 views

Does top read some system files?

If I am correct, the output of free comes from reading /proc/meminfo. In the output of top, is the summary of memory part not specific to a process also coming from /proc/meminfo? which system ...
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1answer
15 views

Do RES and USED of a process include the cache and buffer of the process?

In the output of top, I heard that RES of a process is the part of RAM occupied by the process, and includes the process' code, data, and shared libraries which are in RAM. I wonder if RES of a ...
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0answers
17 views

Understanding shared objects in virtual memory, in the output of top

In the output of top, does SHR for a process consist of only the following parts all the shared objects in RAM, e.g. shared libraries and shared data in RAM, shared between the process and any ...
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1answer
18 views

How to show USED in the output of top?

top doesn't show USED (a part of virtual memory) by default. How can I make it visible? Thanks.
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2answers
42 views

What does it mean that a page fault may or may not involve auxillary storage access in making that page available

From manpage of top nMaj -- Major Page Fault Count The number of major page faults that have occurred for a task. A page fault occurs when a process attempts to read from or ...
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2answers
164 views

Differences and relations between VIRT and USED in output of top?

From manpage of top VIRT -- Virtual Memory Size (KiB) The total amount of virtual memory used by the task. It includes all code, data and shared libraries plus pages that ...
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0answers
47 views

Read another processes memory using ptrace() in C/CPP [RaspberryPi]

So, initially, process A created a file containing data (37 Bytes) read from a stream(UART). Process B has to acquire that data, which is stored in /dev/shm. Process A has an absolute maximum of 4ms ...
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0answers
24 views

Strange PFN read from pagemap

I m trying to find the physical page to which a range of virtual addresses are mapped in a piece of C code that I ve written. I m using the /proc/self/pagemap to read the mapping. I ve used the code ...
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0answers
41 views

Pagemap on memory mapped devices not working

I am trying to find the physical addresses of heap variables, stack variables and memory mapped peripheral addresses using the /proc/{pid}/pagemap file using the steps detailed in the file: http://lxr....
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0answers
12 views

How to mmap file w/ HUGE_PAGES to specific memory location (via “memmap=4G$4G”)

Presently working: Device driver to mmap to specific memory location (isolated by boot parameter "memmap=4G$4G") via the remap_pfn_range call. Desired solution: Same/similar outcome using 2M pages ...
3
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1answer
34 views

How does Linux manage “simultaneous” writes to swap/disk partitions in virtual memory?

I'm currently working on an educational operating system called Pintos. While implementing virtual memory, one of the issues that I'm having is writing data to swap in a page fault that happened while ...
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0answers
15 views

What is the on-demand mapping in the kernel virtual memory in Linux? [duplicate]

In the OS lecture, the lecturer explained that not all the physical memory will fit into virtual address space on a 32-bit architecture. So what the kernel can do is map anything else above 896MB ...
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0answers
30 views

Why does .text region of shared libraries is not flagged as VM_SHARED?

When I'm using shmem/mmap to share memory between processes I can see with pmap that it creates virtual memory area that marked as shared. Example: Address Kbytes RSS Dirty Mode ...
1
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1answer
45 views

vmstat -s command fields meaning, specially “pages paged in” vs “pages swapped in”

Most of the fields are understandable but can someone please explain me the difference between "pages paged in" and "pages swapped in"?. I'm pretty sure that swapping is when the entire process is ...
1
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0answers
75 views

Does Linux maintain a system RAM high water mark?

I know there is VmHWM entry in each process's /proc/[PID]/status file, however is there an aggregate of this that contains the high water mark for the system? I understand the free command give the ...
3
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2answers
109 views

C++ app. with mmap kills kernel? (kernel panic with mmap)

In my C++ program where intensive disk, network I/O and even CPU computation occur, I am using memory mapped region as an array. With very small data, it works fine. However when I ran the program ...
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0answers
53 views

Transparent Huge Pages, Pagetable size and /proc/<pid>/status

TL;DR; My pagetable is far bigger than it should be when using transparent huge pages (THP). I have a program (see below), that allocates 50 GiB of memory, requests transparent huge pages and faults ...
1
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1answer
62 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, 1....
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0answers
16 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 ...
0
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1answer
79 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
votes
1answer
165 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
68 views

Linux kernel running only with use of physical address

Is it theoretically possible to make Linux which for its own kernel (include modules) uses only physical addresses? (it means it completely omits MMU) For processes how would you know if there was ...
-1
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1answer
54 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?
0
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2answers
31 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
16 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
589 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
47 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 ...
2
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0answers
59 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: http:...
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1answer
2k views

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

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
89 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. ...
2
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0answers
64 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?
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2answers
146 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 ...
1
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2answers
210 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
320 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++....
2
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0answers
49 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?
3
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2answers
370 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
361 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 ...
1
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0answers
65 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
151 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
130 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 ...
3
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1answer
167 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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1answer
118 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 ...
1
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1answer
254 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)?