What's Going On In My System's Memory ?

Ever wonder what's going on in your system's memory (RAM) ? Solaris provides a mdb dcmd ::memstat , which provides the status of all the pages in memory. Following is an example of "memstat" in action on my Solaris 10 machine.

jalandhar% su
Password:
# memstat
# mdb -k
Loading modules: [ unix krtld genunix specfs dtrace ufs sd ip sctp usba  fctl nca nfs audiosup random sppp ptm ipc ]
> ::memstat
Page Summary                Pages                MB  %Tot
------------     ----------------  ----------------  ----
Kernel                      13643               106    5%
Anon                        43533               340   17%
Exec and libs                8669                67    3%
Page cache                   5757                44    2%
Free (cachelist)            23950               187    9%
Free (freelist)            163652              1278   63%

Total                      259204              2025
Physical                   255368              1995

Similarly, there is another tool, pmap, that can be used to look at the address space mapping of a process. "pmap" is one of the /proc file-system based utility and provides output as follows. See "man pmap" for more detail.

jalandhar% pmap 791
791:    /bin/ksh -p /usr/sfw/bin/mozilla
00010000     200K r-x--  /usr/bin/ksh
00052000       8K rwx--  /usr/bin/ksh
00054000      48K rwx--    [ heap ]
FF280000     848K r-x--  /lib/libc.so.1
FF364000      32K rwx--  /lib/libc.so.1
FF36C000       8K rwx--  /lib/libc.so.1
FF38E000       8K rwxs-    [ anon ]
FF398000      16K r-x--  /platform/sun4u/lib/libc_psr.so.1
FF3A0000      24K rwx--    [ anon ]
FF3B0000     176K r-x--  /lib/ld.so.1
FF3EC000       8K rwx--  /lib/ld.so.1
FF3EE000       8K rwx--  /lib/ld.so.1
FFBFC000      16K rw---    [ stack ]
total      1400K

posted by Amandeep 5/29/2006 02:12:00 PM | PERMALINK

C Macro For Printing Filename And Line Number

Most C compilers provide the macros __FILE__ and __LINE__ that can be used to print the source file name and line number respectively. These macros come in handy when printing debug information or when using printf() as a general purpose tool for debugging. Imagine a program that allocates memory via malloc(). As a good programming practice, before using the pointer returned by malloc() it has to be ensured that the allocation succeeded (i.e. the pointer returned by malloc() is not NULL). If the memory allocation fails, the program will probably have to give a message indicating this. Now, there can be several malloc() calls through out the program - which one failed? Well use of __FILE__ and __LINE__ macros make it easy to find.

Similarly, a statement like: "printf("%s:%d\n", __FILE__, __LINE__); " , if used appropriately can be used to follow the flow of a program. Ofcourse, this is a crude way of doing something that can be easily done through any standard debugger, without having to change code. Nonetheless, it can come in handy depending on the situation.

posted by Amandeep 5/15/2006 11:19:00 PM | PERMALINK