Re: Why linux memory management isn't clever, always hold large memroy?
bowen wrote:
> Previously, memory use looks good. And I use mysql> load data infile
> 'file' into table to import a very large mysql data file. So the
> memory used became large quickly and soon exhaust all the memory to
> use swap space. After that the system became slow for cpu fully
> waiting IO status. (Why mysql or system do not automatic free some of
> the loaded data from memory, Just use a little swap space to sawp out
> a little memory). After a long time, the mysql load process complete
> and I restart the mysqld daemon, but the memory does still hold large
> memory.
>
> Why linux does not release the memory again ? Is there any way that I
> can free the memory without reboot machine?
>
> Thanks....
>
> shell# free
> total used free shared buffers cached
> Mem: 516488 459376 57112 0 8 420152
> -/+ buffers/cache: 39216 477272
> Swap: 1023992 80 1023912
>
>
> top - 11:20:56 up 46 min, 1 user, load average: 0.00, 0.00, 0.11
> Tasks: 50 total, 1 running, 49 sleeping, 0 stopped, 0 zombie
> Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si,
> 0.0%st
> Mem: 516488k total, 459316k used, 57172k free, 8k buffers
> Swap: 1023992k total, 80k used, 1023912k free, 420084k cached
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 4002 root 16 0 2228 1124 868 R 0.3 0.2 0:00.02 top
> 1 root 16 0 1940 660 564 S 0.0 0.1 0:01.28 init
> 2 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
> 3 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
> 4 root 10 -5 0 0 0 S 0.0 0.0 0:00.02 events/0
> 5 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 khelper
>
It doesn't necessarily make sense to reallocate memory unless it is
actually needed. Reallocation when it isn't required can slow down
other processes.
Of course, there is another possibility, and that is that mysql has a
memory leak somewhere. If you are concerned that it may, I'd suggest
either a message to the mysql maintainer with your observations or grab
the code and run a trace yourself.
T.J.
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