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2
votes
1answer
1k 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 ...
4
votes
0answers
31 views

Shared executable memory [migrated]

I have this short snippet of C: const char *name = "/asdf"; int desc = shm_open(name, O_RDWR | O_CREAT, 0777); ftruncate(desc, 4096); void *block = mmap(NULL, 4096, PROT_EXEC, MAP_SHARED, desc, 0); ...
2
votes
1answer
523 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 ...
0
votes
0answers
21 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
46 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 ...
9
votes
2answers
505 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
32 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 ...
1
vote
2answers
343 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 ...
0
votes
2answers
117 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, ...
2
votes
0answers
336 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 ...
0
votes
0answers
72 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
1k 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 ...
1
vote
0answers
76 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
votes
1answer
466 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
274 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
950 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
votes
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
502 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
812 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: ...