mmap() question

[rozhuk.im at gmail.com]

> > I have a program which mmap()s a lot of large files (total size more
> that RAM and I have no swap), but it needs only small parts of that
> files at a time.
> >
> > My understanding is that when using mmap when I access some memory
> region OS reads the relevant portion of that file from disk and caches
> the result in memory.  If there is no free memory, OS will purge
> previously read part of mmap'ed file to free memory for the new chunk.
> >
> > But this is not the case.  I use the following simple program which
> gets list of files as command line arguments, mmap()s them all and then
> selects random file and random 1K parts of that file and computes a XOR
> of bytes from that region.
> > After some time the program dies:
> > pid 63251 (a.out), uid 1232, was killed: out of swap space
 
My PR with same: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=195882
"this is not bug" - say some devs.