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From: Oliver Welter (mail_at_oliwel.de)
Date: Fri 26 Aug 2005 - 10:26:50 BST


Hi Helmut,

>> well, you can certainly do that, and I guess most apps
>> will handle that perfectly well, unfortunately there
>> are certain apps which tend to allocate huge amounts
>> of virtual memory, just in case they'll need it later
>> on, and those will be really suprised, once they reach
>> the RSS limit and get killed off by the OOM killer.
>
>
> What means 'killed off'? Naively I assumed, that if e.g. current RSS of
> the context is 52 MB and something (e.g. start of a Java application)
> tries to get 42 MB, some pages must be 'kicked out' of real memory to
> fullfill the 64 MB limit, resulting in bad performance, but not 'killed'.

In this case it is likely that simply your new process wont start, you
get in real problems if you run into rss limit for an already running
process: A process P tells the kernel to reserve e.g 40 MB of RAM but
instantly only needs 20 MB, now you fill up the remaining 44 MB of
physikal RAM with other process. When now the R want's the already
reserved space there is nothing you can give him. Now eiter P terminates
because it cant allocate the mem it needs or the OOM Killer process
tries to sweep out processes from the RAM. It is very likely that it
will kill some currently idle processes that are essential for your
system....(I had this last week when OOM killed my mysql and silently my
sshd...)

Oliver

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