Strange Virtual Memory Mapping...!

From: Arijit Das (Arijit.Das_at_synopsys.com)
Date: 09/30/05

  • Next message: Arijit Das: "RH30: Virtual Mem shot heavily by locale-archive..." 
    Date:	Fri, 30 Sep 2005 18:28:58 +0530
To: <linux-kernel@vger.kernel.org>

    I have RH3.0 installed in an AMD64 machine.
     
    In this system, when I look at the virtual address space mappings of a
    process (say a sleep process), I see quite a few strange memory region
    mappings which are neither readable, nor writable/executable and all of
    them are Private (i.e. unshared). Check this:
     
          1024 ---p /lib64/tls/libc-2.3.2.so
          1024 ---p /lib64/tls/libm-2.3.2.so
          1024 ---p /lib64/tls/librtkaio-2.3.2.so
          1024 ---p /lib64/tls/libpthread-0.60.so
     
    On the other hand, when I look at the same info in a Rh7.2 system, I
    don't see anything like that...
     
    Question: How do I make sense of an unreadable/unwritable/unexecutable
    privately mapped memory region? What is its usage? It looks like a 100%
    wastage of the process's address space. How is the process using it? Any
    idea...anybody?
     
    You can find the sample "sleep" commands below.
     
    Thanks,
    Arijit
     
    RH3.0 on AMD64:
    =============
    vgamd126:arijit>sleep 400 &

    [1] 19916
    vgamd126:arijit>pmap 19916
     Size (KB) Perm Associated files (if any)
    ========== ==== =============================================
            16 r-xp /bin/sleep
             4 rw-p /bin/sleep
           132 rwxp
          1108 r-xp /lib64/ld-2.3.2.so
             4 rw-p /lib64/ld-2.3.2.so
             4 rw-p
           540 r-xp /lib64/tls/libm-2.3.2.so
          1024 ---p /lib64/tls/libm-2.3.2.so
             4 rw-p /lib64/tls/libm-2.3.2.so
             4 rw-p
            36 r-xp /lib64/tls/librtkaio-2.3.2.so
          1024 ---p /lib64/tls/librtkaio-2.3.2.so
             4 rw-p /lib64/tls/librtkaio-2.3.2.so
            64 rw-p
          1260 r-xp /lib64/tls/libc-2.3.2.so
          1024 ---p /lib64/tls/libc-2.3.2.so
            20 rw-p /lib64/tls/libc-2.3.2.so
            16 rw-p
            60 r-xp /lib64/tls/libpthread-0.60.so
          1024 ---p /lib64/tls/libpthread-0.60.so
             4 rw-p /lib64/tls/libpthread-0.60.so
            20 rw-p
         31396 r--p /usr/lib/locale/locale-archive
            24 rw-p
    Total Virtual Memory = 38816 KB
    vgamd126:arijit>
     
     
    RH7.2 in i686
    ==========
    eurika120:arijit>sleep 400 &

    [1] 11065
    eurika120:arijit>pmap 11065
     Size (KB) Perm Associated files (if any)
    ========== ==== =============================================
            12 r-xp /bin/sleep
             4 rw-p /bin/sleep
             8 rwxp
            88 r-xp /lib/ld-2.2.4.so
             4 rw-p /lib/ld-2.2.4.so
             4 r--p /usr/lib/locale/en_US/LC_IDENTIFICATION
             4 r--p /usr/lib/locale/en_US/LC_MEASUREMENT
             4 r--p /usr/lib/locale/en_US/LC_TELEPHONE
             4 r--p /usr/lib/locale/en_US/LC_ADDRESS
             4 r--p /usr/lib/locale/en_US/LC_NAME
             4 r--p /usr/lib/locale/en_US/LC_PAPER
             4 r--p /usr/lib/locale/en_US/LC_MESSAGES/SYS_LC_MESSAGES
             4 r--p /usr/lib/locale/en_US/LC_MONETARY
            24 r--p /usr/lib/locale/en_US/LC_COLLATE
             4 r--p /usr/lib/locale/en_US/LC_TIME
             4 r--p /usr/lib/locale/en_US/LC_NUMERIC
             4 rw-p
           136 r-xp /lib/i686/libm-2.2.4.so
             4 rw-p /lib/i686/libm-2.2.4.so
            28 r-xp /lib/librt-2.2.4.so
             4 rw-p /lib/librt-2.2.4.so
            40 rw-p
          1224 r-xp /lib/i686/libc-2.2.4.so
            20 rw-p /lib/i686/libc-2.2.4.so
            16 rw-p
            52 r-xp /lib/i686/libpthread-0.9.so
            32 rw-p /lib/i686/libpthread-0.9.so
           172 r--p /usr/lib/locale/en_US/LC_CTYPE
            24 rwxp
    Total Virtual Memory = 1936 KB
    eurika120:arijit>
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