Am Fr, 11.02.2011, 16:46, schrieb Michael Peters: > On 02/11/2011 09:26 AM, Torsten Förtsch wrote: > >> What does that mean? >> ==================== >> >> The total size of a process comprises its complete address space. >> Normally, by >> far not everything of this space is present in RAM. > > I'm not sure I'm understanding you correctly here, but are you saying > that most of the time not all of a process's memory space is in hardware > RAM? If you are saying that, then I would disagree, at least in the > context of httpd/mod_perl. Most of the time (if not all the time) the > goal should be to have enough RAM that your httpd processes completely > fit into memory. > > Or am I missing something? > > -- > Michael Peters > Plus Three, LP >
I didnt have time yet to read Torsten's post (will do later) but I will take a stab at this question. You are missing the difference between address space and used memory. Sample extract from /proc/*/smaps: Size: 884 kB Rss: 536 kB Pss: 17 kB Shared_Clean: 536 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 0 kB Referenced: 536 kB Swap: 0 kB In this case the address space has a size of 884 kb. Only 536 kb are used though (Rss/Referenced). All of this space is shared. As you can see the difference between 884 kb and 536 kb is not swapped out but just not allocated. Relying on smaps is a little complicated because the format differs with the kernel version. I usually use (just) Private_Dirty to determine if an apache process should be restarted. Its hard to find good thresholds though. Hendrik
