Memory Leak
Hongwei Li
hongwei at wustl.edu
Thu Feb 10 18:15:19 UTC 2005
> Hongwei Li wrote:
>>>On Thu, Feb 10, 2005 at 10:15:39AM +0100, DafyddHugh wrote:
>>> > Hi,
>>> >
>>> > I am running Fedora Core 3 on a machine with 512Mb memory.
>>> >
>>> > There are 2 problems
>>> >
>>> > 1. When the physical memory is exhausted the system tries to use
>>> swap,
>>>the disk spins and the system becomes unusable. This is under
>>>investigation, but any ideas would be appreciated.
>>> >
>>> > 2. More of an issue. Every few minutes (4 or 5) the available
>>> physical
>>>memory decreases by 64k, while the cache memory increases by 4k or 8k.
>>>This is happening on a very "lean" machine (see simple ps post below).
>>>No processes seem to be increasing memory at the same time. Usually the
>>>machine also runs httpd, mysqld, popfile in addition to the posted ps.
>>>It looks like a memory leak, but I can't find the offending process -
>>>any ideas?
>>>
>>>Which kernel version are you running ?
>>>What does the output of free, and slabtop look like ?
>>>
>>> Dave
>>
>>
>> I have a similar question as 2 above. My system: 2.6.10-1.741_FC3
>> The free command displays the free physical memory decreasing
>> continuesly
>> every minute or so:
>>
>> # free
>> total used free shared buffers
>> cached
>> Mem: 1035788 1017952 17836 0 296172
>> 81224
>> -/+ buffers/cache: 640556 395232
>> Swap: 1052216 8120 1044096
>>
>> # free
>> total used free shared buffers
>> cached
>> Mem: 1035788 1017980 17808 0 296228
>> 81244
>> -/+ buffers/cache: 640508 395280
>> Swap: 1052216 8120 1044096
>>
>> # free
>> total used free shared buffers
>> cached
>> Mem: 1035788 1018100 17688 0 296260
>> 81300
>> -/+ buffers/cache: 640540 395248
>> Swap: 1052216 8120 1044096
>>
>> Is it normal? I don't know what will happen if the free memory goes to
>> zero, but it seems that, in my system, it never goes to zero. At some
>> point, it jumps up a little. Please note, my this system is a testing
>> system, only 2 regular users were set up, and only 1 user is checking
>> the
>> testing emails (plus root's shell). It was just rebooted 2 days ago:
>>
>> # top
>> top - 11:51:21 up 1 day, 21:36, 3 users, load average: 0.00, 0.00,
>> 0.00
>> Tasks: 90 total, 1 running, 86 sleeping, 0 stopped, 3 zombie
>> Cpu(s): 0.3% us, 0.0% sy, 0.0% ni, 99.3% id, 0.0% wa, 0.3% hi,
>> 0.0% si
>> Mem: 1035788k total, 1018564k used, 17224k free, 296420k buffers
>> Swap: 1052216k total, 8120k used, 1044096k free, 81360k cached
>>
>> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
>> 10847 root 16 0 3632 948 756 R 0.7 0.1 0:00.07 top
>> 3438 root 16 0 3940 580 492 S 0.3 0.1 0:17.43 nifd
>> 3938 root 16 0 7756 4848 1612 S 0.3 0.5 1:11.28 hald
>> 1 root 16 0 2756 560 480 S 0.0 0.1 0:00.82 init
>> 2 root 34 19 0 0 0 S 0.0 0.0 0:00.08 ksoftirqd/0
>> ...
>>
>> Why does it take almost all of 1Gb physical ram?
>
> The kernel will attempt to use any available memory for buffering and
> cacheing, as this makes things run faster. When applications need more
> memory, buffer and cache space is released. So the figure you need to
> look at in the "free" output is the one in the row marked "-/+
> buffers/cache:", which shows memory usage not in buffers and cache; that
> represents how much memory you're "really" using. In your example above,
> the last run of "free" actually showed more free memory than the first
> one.
>
> Paul.
>
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Thank you very much for help!
Hongwei Li
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