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7 views

Communication between two kernel drivers [migrated]

I have custom embedded hardware i'm working on which runs linux. I've implemented a spi kernel driver to handle spi access to a eeprom which is exposed to userspace. Now i have another kernel driver ...
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0answers
14 views

Can ramdisk improve performance when stats show low wait and system cpu use?

I have jobs that do I/O of rates peaking around 200mb/s. On high load (over twice cpu cores) I tried to copy large file and got only few mb/s. Gathered dstat show single digits in wai and sys category ...
6
votes
1answer
33 views

File backed, locked shared memory and disk interaction

Varnish, a HTTP accelerator, uses a ~80MB file backed SHM log that is mlock()ed into memory. The Varnish docs recommend to store the file on tmpfs to avoid unnecessary disk access. However if the ...
2
votes
1answer
410 views

can not create /dev/shm

I need to create /dev/shm on an embedded ARM system. From "Installed The Latest Changes to Current and......". I see that it can be created with mkdir /lib/udev/devices/shm, but I'm wondering what ...
9
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2answers
405 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 ...
3
votes
1answer
31 views

Grsecurity subject mode x

I am conducting some research on Grsecurity on Hardened Gentoo, see http://en.wikibooks.org/wiki/Grsecurity. To be more specific, I am trying to find an example where subject mode x makes a ...
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2answers
286 views

Hugepages in linux - how to make sure that java process will start using hugepages

I'm running java server on Red Hat Enterprise Linux Server release 5.9. Recently I started to use HugePages as it has some advantages I would like to use. System was configured correctly (as many ...
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2answers
116 views

Why is there no critical section in the pipe?

Why is there no critical section in the pipe? For example, as in shared memory. In pipe have general data, which in common use in joint processes, but in the shared memory also have general data, ...
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0answers
301 views

Resize / remount /dev/shm not working

I've got a linux box dedicated to playing host to an Oracle server installation. It's got 4Gb RAM and by default, 50% (2Gb) has been allocated to /dev/shm. I want to change this to 3Gb, but I am ...
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0answers
68 views

Permission in shmget Linux

I've been searching about 0666 permission in shmget(). I know that 0666 permission will grant read & write permission on the shared memory segment. But, how do I prove it have permission if I ...
3
votes
1answer
875 views

operation in /dev/shm causes overflow

I am repeating tens of thousands of similar operations in /dev/shm, each with a directory created, files written, and then removed. My assumption used to be that I was actually creating directories ...
2
votes
1answer
909 views

use `/run/shm` (formerly `/dev/shm`) as a temp directory

Is it good practice to create a directory in /run/shm (formerly /dev/shm) and use that like a temp directory for an application? Background: I am writing black box tests for a program which does a ...
1
vote
0answers
75 views

Viewing shared segments created by shmget

I'm trying to "visualize" shared memory between two processes. I've created a little server-client example where the client writes some data to a shared memory location and the server reads from it. ...
11
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1answer
423 views

What is the difference between shared memory in early unix systems vs modern unix systems?

How could processes share memory in early versions of UNIX version modern implementations of shared memory?
0
votes
2answers
267 views

Linux - get shared memory values from Perl script

I'm trying to get shared memory information from a linux box. I'm looking for shmmax, shmmni, shmall, msgmax, msgmni, semmsl, semmns etc. How to get all those values from a Perl script. any help is ...
5
votes
1answer
925 views

What is “SYSV00000000”?

In my dmesg this appeared when my window manager (xfwm4, part of XFCE) crashed: xfwm4[3936]: segfault at 7f3c7c523770 ip 00007f3c7c523770 sp 00007ffffea1ee28 error 15 in SYSV00000000 ...
4
votes
1answer
2k views

What are shmpages in laymans terms?

What exactly are shmpages in the grand scheme of kernel and memory terminology. If I'm hitting a shmpages limit, what does that mean? I'm also curious if this applies to more than linux
3
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3answers
1k views

Share memory between a virtual machine and the host

Through shmget and shmat, I am able to access the data stored in one program from another program. Here's the gist of the code: key=ftok("shared.c",'c'); shmid=shmget(key,1024,0644|IPC_CREAT); ...
3
votes
2answers
491 views

IPC: Shared memory killed process notification

In shared memory system, when two processes share a shared memory segment, after one process is killed, how will the other running process be notified of the killed process by the shared memory system ...
4
votes
1answer
806 views

Linux - why is kernel.shmall so low by default?

I run DB2 on Linux where I have to allocate the vast majority of memory on the machine to shared memory segments. This page is typical of the info that I've found about shmall/shmmax: ...