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Re: Linux2.6 overcommit behaviour

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Linux2.6 overcommit behaviour
Date: 2003-09-01 02:37:58
Message-ID: 3F52B106.8030600@dunslane.net (view raw or flat)
Thread:
Lists: pgsql-hackers

Bruce Momjian wrote:

>Andrew Dunstan wrote:
>  
>
>>I believe that the swap slot can be subsequently freed, though. In 
>>theory your available virtual memory should be (almost) RAM+swap. In 
>>practice, Linux can run too close to that limit, (or way over it if you 
>>turn the checks off). But restricting the maximum possible pages to 
>>RAM/2 + swap should normally be fine. IANAKH, though.
>>
>>Also note that the truly bad thing about the OOM killer is that it can 
>>affect a process that is not making any new memory demands at all.
>>    
>>
>
>How does the OOM killer kill processes, kill -9 or kill -1 and wait?
>  
>

It sends a SIGKILL (9) unless the process is doing raw io, in which case 
it sends SIGTERM (15). It can't really wait - at this stage the kernel 
is in trouble - it can either kill processes or panic. The whole idea of 
strict accounting is not to let it get to this stage in the first place.

see mm/oom_kill.c

cheers

andrew


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