The virtual-memory tag has no wiki summary.
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56 views
How does kernel know, which pages in the virtual address space correspond to a swapped out physical page frame? [migrated]
Consider the following situation: the kernel has exhausted the physical RAM and needs to swap out a page. It picks least recently used page frame and wants to swap its contents out to the disk and ...
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0answers
16 views
Is ZONE_NORMAL mapped on the kernel space only?
In several textbooks I've stumbled upon a strange phrase, that "if the amount of physical RAM available is small, the ZONE_HIGH might not exist at all and all the memory would belong to ZONE_NORMAL".
...
0
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1answer
44 views
Why is brk(0) called?
On a first shell I run the command tail with no argument.
On a second shell I kill the first tail using strace to monitor the system calls.
qdii@nomada ~ $ strace kill 1713
execve("/bin/kill", ...
1
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3answers
55 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 ...
2
votes
2answers
99 views
Where is the virtual memory stored on hard drive?
If a process wants to access a memory address that is not in physical memory, the OS outsources a page frame from physical memory to the hard drive for later use. Where on the hard drive is this data ...
0
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1answer
91 views
Do USB emulators exist for Linux?
I'm looking for software that lets me have many virtual USB drives on my Ubuntu installation. I want them to be seen by virtual machines in VirtualBox so I can do backup operators. I need the drives ...
1
vote
1answer
55 views
What information exactly is in the access control bits of a page table?
I'm currently learning for an exam in operating systems. This includes learning some basics about page tables, which lead me to the question Why using hierarchical page tables? which mentions that ...
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0answers
51 views
pmount is not mounting Virtual Hard Disk
well , I'm using pmount for mounting usb devices .
I had made virtual hard disk on my virtual servers to check backup operations on them .
here's the problem :
pmount is not accepting to mount ...
2
votes
1answer
151 views
Huge page and performance improvemnt
How can using huge page improve performance?
I have read that huge pages improve performance by reducing TLB lookups and reducing the size of the page table. Can someone tell me how this helps with ...
1
vote
2answers
73 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 ...
1
vote
2answers
201 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 ...
5
votes
3answers
375 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 ...
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0answers
152 views
Where does the Linux kernel reside in memory ?
From some book I have, I have in my notes that the Linux kernel resides at 0xc00000000 on 32-bit systems, and is mapped into user space for performance reasons.
Is this accurate ? How can I verify ...
3
votes
2answers
101 views
Misleading explanation of Virtual Memory in TLDP
I'm completely confused about explanation of virtual memory in TLDP:
http://www.tldp.org/LDP/tlk/kernel/processes.html#tthFtNtAAB
They say:
Each individual process runs in its own virtual ...
0
votes
1answer
86 views
What does m represents in VIRT column using TOP command
When we run top command it shows all the processes information. But under VIRT column there is m written against some values what does that m represents, is it MB . If yes then why it is only showing ...
4
votes
3answers
116 views
What is contained in these addresses?
I am working on MUlti-processor record-replay feature of a virtual machine.
I have a log of non-deterministic memory access done in the virtual machine by virtual CPUs.
A very high proportion of these ...
0
votes
1answer
490 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 is ...
-1
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2answers
277 views
What would be a light weight, memory non-intensive distro for virtual server use?
I have come across several posts talking about light weight distros from a general context, but none of them are really hitting the nail on the head for me.
Specifically, I have PHP script that I run ...
3
votes
1answer
934 views
How to debug Linux kernel panic?
I am trying to debug a kernel panic. Panic message says unable to handle kernel paging request for address 40025694.
At the time of panic it was executing ldreq r10, [lr, #-4] @ get SWI instruction. ...
6
votes
2answers
647 views
An oom killer thats baffling me
I am not able to understand why would kernel issue this oom killer when I see enough memory is available:
Also why are there so many kernel cache pages allocated?
I say enough memory is available ...
3
votes
1answer
252 views
Rationale for making user space text segment start at 0x8048000
I read somewhere that (at least since Linux v. 2.6) all user-space code is placed at load address 0x8048000 in the virtual memory address space.
My own observations confirm this. I have done a
cat ...
1
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2answers
149 views
Sudden burst in free memory
I'm experiencing some strange memory management behaviour on Squeeze with Kernel 2.6. I'm trying to get to the bottom of this with nmon.
Sometimes this will freeze up the system for 30 seconds to 5 ...
1
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0answers
280 views
Memory mapping of the Linux kernel : 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 ...
2
votes
1answer
96 views
Memory Management: Faulting virtual addresses
I came across the following on http://tldp.org/LDP/tlk/mm/memory.html
If the faulting virtual address is invalid this means that the process
has attempted to access a virtual address that it ...
1
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2answers
311 views
NAND flash memory wear & virtual memory page swap
For a linux kernel with virtual memory and disk storage, pages are swapped back and forth into swap area. But embedded systems generally use NAND flash instead of disk. A NAND flash has a limited ...
2
votes
2answers
485 views
How much RAM can an application allocate on 64-bit x86 Linux systems?
Is it true that a single application can not allocate more than 2 GiBs even if the system has GiBs more free memory when using a 32-bit x86 PAE Linux kernel? Is this limit loosened by 64-bit x86 Linux ...
2
votes
1answer
257 views
How often is PSS value updated for a given process in /proc/pid/smaps
So if n processes are sharing a library L with size M then the contribution to their PSS is M/n.
Now imagine one of the process terminates. So the contribution would be M/(n-1).
Q1: My question is ...
8
votes
1answer
4k 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
175 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
1answer
394 views
tmpfs and vm.swappiness
I have started tuning a bit Linux VM performance on my system (yes. I know that vm.swappiness=0 will kill kittens but I found 30-40 as much better for me as it improved my latency - probably at cost ...
5
votes
1answer
327 views
User Kernel split in 64bit Linux
What is the default user/kernel split in the 64bit linux ?
I read Documentation/x86_64/mm.txt (which someone pointed out), but I could not make out. Can somebody provide a direct answer (something ...
3
votes
1answer
573 views
Solaris swap allocation with mlocked shared memory
I'm having a hard time understanding how Solaris 10 x86 swap allocations work in the
presence of mlocked share memory.
I wrote a small program that:
Gets a 1G SHM segment (shmget)
Attaches it to ...
1
vote
1answer
2k views
Setting /proc/sys/vm/drop_caches to clear cache
As part of doing some cold cache timings, I'm trying to free the OS cache. The kernel documentation says:
drop_caches
Writing to this will cause the kernel to drop clean caches, dentries and
inodes ...
5
votes
2answers
1k 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 ...
5
votes
1answer
2k 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 ...
2
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3answers
1k views
How is paging managed in the absence of swapping?
How is paging managed in the absence of swapping. If that is the case, how will a page fault be managed?
What I meant is, if there is no availability for swapping, then how is Paging managed. I ...
