NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/unix/question/10765

Internet Message Format | 1992-09-07 | 1.8 KB

Path: sparky!uunet!cis.ohio-state.edu!ucbvax!sequent.cc.hull.ac.uk!S.Marshall
From: [e-mail] (Simon Marshall)
Newsgroups: comp.unix.questions
Subject: Does free() really free?
Message-ID: <[e-mail]>
Date: 5 Sep 92 17:17:25 GMT
Sender: [e-mail]
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Or: How do I find out the real size of a running process?

    Hi all.  This is really a question about the Sequent's shfree(), but
    in tests it seems to apply to other machines and free() in general.
    Please can anyone give a knowledgable answer?

    If I malloc(), then free(), the SZ (SIZE) column of ps does not show
    the expected fall.  I don't believe that the system ignores freed space,
    but then again I know that software that I have written thrashes
    machines, despite the fact that most of the memory malloc()ed is
    subsequently free()ed.

    On our Sequent and Suns, for example, once the SZ column shows
    70Meg+, you can see the machines thrash.  But I can work out that the
    actual unfreed memory only amounts to at most 15Meg.

    So, please could anyone tell me what is going on here?  Does free()
    actually free, and is the SZ column of ps reliable in any way?  Or is
    free() working as expected, ps lying, but 15Meg is too much?  Surely
    not?!  I'd welcome anything emailed/posted.  (Except unhelpful questions
    of the order `why are you mallocing then freeing so much' etc. :-)

    Thanks in advance, Simon.
_______________________________________________________________________________
Simon Marshall, Dept. of Computer Science, University of Hull, Hull HU6 7RX, UK
  "Football isn't about life and death.  It's more important than that." Bill
Email: [e-mail]    Phone: [phone]    Fax: 466666   Shankley