All about using memory mapped files. Questions on programming should be asked on Stack Overflow SE.

learn more… | top users | synonyms

1
vote
1answer
38 views

How does mmap'ing /dev/mem work despite being from unprivileged mode?

As far as my understanding goes, User space programs run in the unprivileged mode, and thus do not have direct access to memory or I/O. Then how exactly can we directly access memory or I/O locations ...
1
vote
0answers
21 views

Using shared memory through tmpfs and NUMA on x86_64/Linux

Here's what I'd like to do: put a file on tmpfs but ensure that all of it (all pages of it) ends up on the same NUMA node. First, I thought this would be trivial: I'd just mmap() a tmpfs file with ...
6
votes
1answer
156 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 ...
3
votes
1answer
41 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
1answer
147 views

proc/sys/vm/flush_mmap_pages missing in 3.9 kernel, how to get it?

There was an option in redHat 5.2 called flush_mmap_pages, I could set this to zero and that would turn of writing dirty pages from a mapped memory file (so I can do it myself when I want to). However ...
1
vote
1answer
518 views

Ext4 exhibits unexpected write latency variance vs. ext2

I have a latency sensitive application running on an embedded system, and I'm seeing some discrepancy between writing to a ext4 partition and an ext2 partition on the same physical device. ...
1
vote
0answers
263 views

Problems when using the framebuffer device directly

I am writing a program using the framebuffer device directly and I have three problems there. 1) The only way I can set the screen resolution correct is by passing the kernel option during boot: ...
4
votes
1answer
725 views

Behavior of mmap'd memory on memory pressure

I have a large tar file (60GB) containing image files. I'm using mmap() on this entire file to read in these images, which are accessed randomly. I'm using mmap() for the following reasons: Thread ...
8
votes
3answers
545 views

Memory size for kernel mmap operation

I'm interested in the way Linux mmaps files into the main memory (in my context its for executing, but I guess the mmap process is the same for writing and reading as well) and which size it uses. So ...
5
votes
1answer
2k views

Hung system call

So I'm working with a custom kernel module that I'm writing a python front end for. The kernel module works, and it adds a framebuffer device file to /dev/fb1. I can read and write to it fine. I've ...