Hello,
I have a large dataset, which I want to access in my forks(). I only need to read the data so to save memory I would like to avoid copyOnWrite here.
While I get the "big picture" of copyOnWrite, I still have some places in my code, where copying does take place and I just don't understand why. I am using Linux::Smaps and use some code similar to the example given here, mainly looking at the shared_dirty and private_dirty values.

example: I have an (hopefully shared) array with pointers to (hopefully shared) data arrays. When I do for example

foreach my $arrayPointer (@$pointerList) { };

the shared_invalid value decreases and the private_invalid value increases alot, sometimes several hundred kilobytes. But shouldn't it just read?
I asked google for help and searched here, but somehow I don't find anything to answer my big questions:
- WHY does copying happen
- WHAT can I do to avoid it
- do I even look at the correct variables or should I check other ones? - is there a kind of "copyOnWrite for dummies" document somewhere on the net, if possible perl related?

thanks ahead for sharing your wisdom :)

In reply to WHY copying does happen (fork) by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.