[CentOS] strict memory

Mag Gam magawake at gmail.com
Thu Oct 23 11:17:53 UTC 2008


ulimit is good for per process. What about for total usage? If a user
has 5 processing -- each taking up 10G, will account for 50G. Is there
a way to avoid this? Or have the VM be sensative, once its swapping we
want to start killing the processing that take the most memory?

TIA

On Wed, Oct 22, 2008 at 1:58 AM, Amos Shapira <amos.shapira at gmail.com> wrote:
> 2008/10/17 Mag Gam <magawake at gmail.com>:
>> Hi John:
>>
>> Well, we run a lot of statistical analysis and our code loads a lot of
>> data into a vector for fast calculations. I am not sure how else to do
>> these calculations fast without loading it into memory. Thats why we
>> have to do it this way.
>
> About 15 years ago I changed an application on SGI IRIX from using
> text files scanf(3)'ed into memory
> (with floating point numbers in them) to binary files mmap(2)'ed into
> memory. Processing time was cut down by over 95% and did much more in
> the 5% left (e.g. allow interactive real-time viewing of different
> "frames" of data).
>
> Using mmap'ed files means that the system will know that these pages
> are backed by blocks on the file system and therefore it won't take up
> so much "buffer" space which needs to be writen out into the swap
> partition whenever the memory buffer is needed for something else,
> only disk cache space which can be just freed if the buffer was only
> read. You can also benefit if multiple processes access same file -
> they'll share the buffer in memory too.
>
> It's not a silver bullet, there are still issues with too random
> access causing the system the thrash, but at least it won't take up so
> much swappable memory, it'll save lots of copying (file->kernel->user
> when reading and the other way around when writing), system calls etc.
>
> If you can process data in sequential order and possibly with help of
> madvise(2) you can probably squeeze out even more from this option.
>
> --Amos
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