On 09/27/2012 01:57 AM, Jérémie Dubois-Lacoste wrote: > We have a computing cluster running Sun Grid Engine, which > considers this value to check if a process exceeds the memory > limit or not. So somehow I'm bound to consider it. > > I installed a machine from scratch with CentOS 6.2 x64, nothing > else, I open a terminal, I run this simple bash script and VIRT > goes beyond 100MB for it. > I understand it may not be very precise, however I still don't > understant the difference compared to other x64 ditributions, > under CentOS the value is 7 times higher! OK, so compare the memory map of the process on the two systems. For example, I've included the output of 'pmap $$' on two CentOS 6 systems. One is 32bit, the other is 64. VIRT on the 32 bit system is ~5MB. On the 64 bit system, VIRT is ~116MB. Why? Well, most of the VIRT size is a mmapped file, /usr/lib/locale/locale-archive. That file isn't resident in memory for the most part, but because the process addresses the contents of that file as if they were memory, rather than as if the content were a file, it's accounted as part of the VIRT size. My login shell on the 64 bit host is only using 3.5MB of RAM total (including libraries shared with other processes), but its VIRT size is ~116MB. If your vendor is using VIRT to make decisions about available resources, they're doing their job profoundly wrong. RES would be better, but still would represent far more memory use than is accurate, especially on systems with many active processes. 64 bit system: [gordon at vagabond:~]$ pmap $$ 23966: bash 0000000000400000 872K r-x-- /usr/bin/bash 00000000006d9000 4K r---- /usr/bin/bash 00000000006da000 36K rw--- /usr/bin/bash 00000000006e3000 24K rw--- [ anon ] 00000000008e2000 36K rw--- /usr/bin/bash 000000000122d000 1836K rw--- [ anon ] 000000383c000000 128K r-x-- /usr/lib64/ld-2.15.so 000000383c21f000 4K r---- /usr/lib64/ld-2.15.so 000000383c220000 4K rw--- /usr/lib64/ld-2.15.so 000000383c221000 4K rw--- [ anon ] 000000383c400000 1712K r-x-- /usr/lib64/libc-2.15.so 000000383c5ac000 2048K ----- /usr/lib64/libc-2.15.so 000000383c7ac000 16K r---- /usr/lib64/libc-2.15.so 000000383c7b0000 8K rw--- /usr/lib64/libc-2.15.so 000000383c7b2000 20K rw--- [ anon ] 000000383cc00000 12K r-x-- /usr/lib64/libdl-2.15.so 000000383cc03000 2044K ----- /usr/lib64/libdl-2.15.so 000000383ce02000 4K r---- /usr/lib64/libdl-2.15.so 000000383ce03000 4K rw--- /usr/lib64/libdl-2.15.so 000000384d000000 148K r-x-- /usr/lib64/libtinfo.so.5.9 000000384d025000 2044K ----- /usr/lib64/libtinfo.so.5.9 000000384d224000 16K r---- /usr/lib64/libtinfo.so.5.9 000000384d228000 4K rw--- /usr/lib64/libtinfo.so.5.9 00007f8ae82aa000 48K r-x-- /usr/lib64/libnss_files-2.15.so 00007f8ae82b6000 2044K ----- /usr/lib64/libnss_files-2.15.so 00007f8ae84b5000 4K r---- /usr/lib64/libnss_files-2.15.so 00007f8ae84b6000 4K rw--- /usr/lib64/libnss_files-2.15.so 00007f8ae84b7000 102580K r---- /usr/lib/locale/locale-archive 00007f8aee8e4000 16K rw--- [ anon ] 00007f8aee8f5000 8K rw--- [ anon ] 00007f8aee8f7000 28K r--s- /usr/lib64/gconv/gconv-modules.cache 00007f8aee8fe000 4K rw--- [ anon ] 00007fff5010a000 132K rw--- [ stack ] 00007fff501ff000 4K r-x-- [ anon ] ffffffffff600000 4K r-x-- [ anon ] total 115904K 32 bit: enetics at firewall:~$ pmap $$ 32629: -bash 00291000 4K r-x-- [ anon ] 00952000 120K r-x-- /lib/ld-2.12.so 00970000 4K r---- /lib/ld-2.12.so 00971000 4K rw--- /lib/ld-2.12.so 00978000 1584K r-x-- /lib/libc-2.12.so 00b04000 8K r---- /lib/libc-2.12.so 00b06000 4K rw--- /lib/libc-2.12.so 00b07000 12K rw--- [ anon ] 00b0c000 12K r-x-- /lib/libdl-2.12.so 00b0f000 4K r---- /lib/libdl-2.12.so 00b10000 4K rw--- /lib/libdl-2.12.so 00b39000 48K r-x-- /lib/libnss_files-2.12.so 00b45000 4K r---- /lib/libnss_files-2.12.so 00b46000 4K rw--- /lib/libnss_files-2.12.so 00b7d000 88K r-x-- /lib/libtinfo.so.5.7 00b93000 12K rw--- /lib/libtinfo.so.5.7 08047000 836K r-x-- /bin/bash 08118000 20K rw--- /bin/bash 0811d000 20K rw--- [ anon ] 08b43000 232K rw--- [ anon ] b7682000 28K r--s- /usr/lib/gconv/gconv-modules.cache b7689000 2048K r---- /usr/lib/locale/locale-archive b7889000 8K rw--- [ anon ] b788f000 12K rw--- [ anon ] bff3f000 84K rw--- [ stack ] total 5204K