Re: Memory intensive processes

Systemkennung Linux (
Wed, 11 Dec 1996 17:47:05 +0100 (MET)

> > Consider you have a process with a very large set of matrices. Most of
> > these could be sparse (eg mostly zeros). The IEEE representation of
> > floating point zeroes is all zeroes. Therefore, the scheme you mention
> > could in fact suitably represent in a single page a large chunk of memory
> > that would otherwise be wasted (filled with zeroes). This alone could get
> > some of the large process blues off of Linux' back.
> >
> This is true. Also the act of READING zero-filled pages should not cause
> a trap to the operating system. Many FFTs null-fill a lot of RAM and
> certainly never write to it.

Not a good idea. Implementing your suggestion would mean that large parts
the page tables which are are just truncated off would have to be allocated
and memory. Just mmaping 1gb from /dev/zero would cost you over 1mb of
*not swappable* memory for page tables. Aside of that allocation and filling
consumes a lot of time.

Better optimize the FFT ...