Re: ten thousand small processes

From: Petri Helenius (pete_at_he.iki.fi)
Date: 06/22/03

  • Next message: Pedram Nimreezi: "RE: ten thousand small processes" 
    To: "D. J. Bernstein" <djb@cr.yp.to>, <freebsd-performance@freebsd.org>
Date: Sun, 22 Jun 2003 11:14:44 +0200

    Have you looked at the malloc manpage and tuned the cache size;

         < Reduce the size of the cache by a factor of two. The default
                 cache size is 16 pages. This option can be specified multiple
                 times.

    > Double the size of the cache by a factor of two. The default
                 cache size is 16 pages. This option can be specified multiple
                 times.

    Pete

    ----- Original Message -----
    From: "D. J. Bernstein" <djb@cr.yp.to>
    To: <freebsd-performance@freebsd.org>
    Sent: Saturday, June 21, 2003 8:58 PM
    Subject: ten thousand small processes

    > FreeBSD 4.8. Test program: malloc(360); malloc(80); malloc(180);
    > malloc(16); malloc(440); sleep(10); _exit(0). Compile statically.
    >
    > The program ends up with 44KB RSS. Where is all that DRAM going? The
    > program also ends up with 168KB VSZ. Where is all that VM going?
    >
    > I don't care much about the 3-page text segment. But I do care about the
    > 39 extra pages of VM, and the 8 extra pages of DRAM. There's no obstacle
    > to having a small program fit into _one_ page per process; two or three
    > can be excused, but 39 is absurd. (Yes, I know that Solaris is worse.)
    >
    > At least 2 pages appear to be wasted by exit(), because it brings in a
    > chunk of stdio, which uses 84 bytes of data and 316 bytes of bss. The
    > libc implementors clearly don't care about 316 bytes of memory, so why
    > don't they make those 316 bytes static? Why doesn't the compiler
    > automatically merge some bss into data when that saves a page? Why can't
    > I omit exit(), manually or automatically, when it's unreachable?
    >
    > Furthermore, malloc() appears to chew up a whole new page of DRAM for
    > each allocation, plus another page---is this counted in VSZ?---for an
    > anonymous mmap. Would it really be that difficult to fit 1076 bytes of
    > requested memory into the 3000-odd bytes available at the end of bss?
    >
    > I sure hope that there's some better explanation for the remaining 32
    > pages than ``Well, we decided to allocate 131072 bytes of memory for the
    > stack,'' especially when I'm hard-limiting the stack to 4K before exec.
    >
    > ---D. J. Bernstein, Associate Professor, Department of Mathematics,
    > Statistics, and Computer Science, University of Illinois at Chicago
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