 | | | No swap being used | No swap being used 2006-01-12 - By William Warren
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aha..software raid. I bet that's the issue. You're simply reaching the
limits of the system. Can you throw a good hardware raid controller in
there and get your RAID off the cpu(which is where software raid resides).
Jeff Macfarland wrote:
> William Warren wrote:
>> It depends on kernel tuning but most times the kernel will start
>> dumping the file cache to free up ram. Once that is done it will
>> start swapping. You pretty much have to chew up all ram before swap
>> stats getting used. If you are having high iowaits then your issue is
>> hdd or IO not swapping. Check your RAID controller or you may just
>> need to upgrade to faster disks.
>
> We're pretty sure its IO as well but are keeping our eyes and ears open.
> We have a case open with Sun about the slowdowns (sunrays are severely
> affected, but ssh prompts seize up briefly as well)
>
> The 14 disks in question are 15k rpm 36G FC drives in an old compaq
> enclosure. Its an older loop device with mdadm handling raid.
>
> I remember back in the day when 2.4.2x kernels were new where I had to
> use some of Ingo Molnar's (sp?) latency patches or else desktop usage
> was pitiful if the machine was doing any sort of IO. I've asked about
> this IO problem before on this list (and elsewhere) and go no replies so
> I figured it was just us experiencing this issue and not for lack of
> kernel latency patches.
>
> IIRC, however, iostat shows high await times on /dev/sda whereas the cvs
> repo is on the fc enclosure (/export) by way of a symlink on /.
>
>>
>> Jeff Macfarland wrote:
>>> Jussi Silvennoinen wrote:
>>>>> Sun V20z, RHEL 3u5, i386 kernel, 12GB RAM, 12GB swap
>>>>>
>>>>> This box hosts quite a few things, among them serving SunRay's. We've
>>>>> been experiencing horrible slowdowns particularly during a cvs
>>>>> checkout.
>>>>> Just noticed that NO swap is being used:
>>>>>
>>>>> output of `free`:
>>>>>
>>>>> total used free shared buffers
>>>>> cached
>>>>> Mem: 12277844 12036764 241080 0 1333552
>>>>> 7502204
>>>>> -/+ buffers/cache: 3201008 9076836
>>>>> Swap: 12578704 0 12578704
>>>>
>>>> I guess yer a Solaris-admin? Things work a bit different in the
>>>> penguin-world.
>>>>
>>>> No need to swap = nothing gets swapped. Solaris does it a bit
>>>> different.
>>>> Over 7gb's of your ram is used for block cache so you're far away
>>>> from actually needing to swap.
>>>>
>>>
>>> At what point will linux start using swap? Where there is absolutely
>>> no free RAM left? Its been my understanding that swap will almost
>>> always be used for idle processes regardless of amount of free ram
>>> left. I see the output of free range from a few gigs free to 50M and
>>> at no point is anything swapped. I suppose I am just used to our old
>>> solaris boxes though.
>>>
>>>> Instead, look at the output of 'top' when the slowdowns occur.
>>>
>>> We have. IO waits perecentage goes quite high and iostat shows
>>> 'await' time on the order of a few thousand ms for sda. The cvs repo
>>> is on a software raid partition though.
>>>
>>> Thanks for the swap info though.
>>>
>>
>
>
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