In the olden days, the Linux enthusiasts would recommend that you should create a SWAP partition that has twice the size of your RAM. Nobody knew why, but it just a rule we all followed. In those days, computers had something like 32 MB of RAM. Using 64 MB of disk space as SWAP seemed OK.
Today I opened a complex diagram in PDF format, generated by a computer program, with the Ubuntu PDF reader, Evince. The last setting Evince used for that file was with a very high zoom level, and so Evince tried to render the PDF page with that zoom level. After a few seconds I lost control of the computer due to thrasing. How can this be? The software security guys keep a constant watch on program flaws that make DoS attacks possible when opening a malicious file. I have generated a DoS attack to myself?!
When I regained control of the computer I discovered I had 3 GB of swap space installed. When a program is buggy and tries to allocate huge chunks of memory, of course it will bring the system to its knees.
My solution: reduce the swap space to 512 MB. Now Evince just fails to allocate memory and does not render the page. But I regain control and can switch to a different zoom level and finally render my page. A lesson learnt.
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About Me
- Gustavo Carneiro
- Telecommunications researcher, PhD student, open source developer, metalhead, and avid scifi/fantasy reader.
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4 comments:
You do not use hibernate, right?
Otherwise you would *need* at least a bit more then the size of your RAM.
Damn :-/
Actually I use hibernate only rarely, as I find it too slow.
But I really cannot stand the way Linux handles misbehaving applications. You give it 3 GB of swap and then it becomes trivial to write an application or file that DoS'es the system.
I think there is some way to cut processes' resources, in order for this not to happen. But maybe it is just a product of my imagination ;-)
There's ulimit. But is a per-process limit. If you limit a process's memory to 1 GB, but you already have 2 GB occupied with 1.5 GB of RAM, that extra 1 GB a new process could allocate might very well thrash the system anyway.
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