Re: Memory Management

["Márcio Oliveira" <moliveira@latinsourcetech.com>]

Neil Horman wrote:

>On Thu, Jul 21, 2005 at 10:40:54AM -0300, Márcio Oliveira wrote:
>  
>
>>>http://people.redhat.com/nhorman/papers/rhel3_vm.pdf
>>>I wrote this with norm awhile back.  It may help you out.
>>>Regards
>>>Neil
>>>
>>>
>>>      
>>>
>>Neil,
>>
>>  Thanks.~10-12GB of total RAM (16GB) are
>>
>>  How can Proc virtual memory parameters like inactive_clean_percent, 
>>overcommit_memory, overcommit_ratio and page_cache help me to solve / 
>>reduce Out Of Memory conditions on servers with 16GB RAM and lots of GB 
>>swap?
>>
>>    
>>
>I wouldn't touch memory overcommit if you are already seeing out of memory
>issues.  If you are using lots of pagecache, I would suggest increasing
>inactive_clean percent, reducing the pagecahce.max value, and modifying the
>bdflush parameters in the above document such that bdflush runs sooner, more
>often, and does more work per iteration.  This will help you move data in
>pagecache back to disk more aggressively so that memory will be available for
>other purposes, like heap allocations. Also if you're using a Red Hat kernel and
>you have 16GB of ram in your system, you're a good candidate for the hugemem
>kernel.  Rather than a straightforward out of memory condition, you may be
>seeing a exhaustion of your kernels address space (check LowFree in
>/proc/meminfo).  In this even the hugemem kernel will help you in that it
>increases your Low Memory address space from 1GB to 4GB, preventing some OOM
>conditions.
>
>
>  
>
>>  Kernel does not free cached memory (~10-12GB of total RAM - 16GB). Is 
>>there some way to force the kernel to free cached memory?
>>
>>    
>>
>Cached memory is freed on demand.  Just because its listed under the cached line
>below doesn't mean it can't be freed and used for another purpose.  Implement
>the tunings above, and your situation should improve.
>
>Regards
>Neil
>
>  
>
>>/proc/meminfo:
>>
>>             total:    used:    free:  shared: buffers:  cached:
>>Mem:    16603488256 16523333632 80154624        0 70651904 13194563584
>>Swap:   17174257664 11771904 17162485760
>>MemTotal:     16214344 kB
>>MemFree:         78276 kB
>>Buffers:         68996 kB
>>Cached:       12874808 kB
>>
>>Thanks to all.
>>
>>Marcio.
>>    
>>

Neil,

   Thanks for the answers!

The following lines are the Out Of Memory log:

Jul 20 13:45:44 server kernel: Out of Memory: Killed process 23716 (oracle).
Jul 20 13:45:44 server kernel: Fixed up OOM kill of mm-less task
Jul 20 13:45:45 server su(pam_unix)[3848]: session closed for user root
Jul 20 13:45:48 server kernel: Mem-info:
Jul 20 13:45:48 server kernel: Zone:DMA freepages:  1884 min:     0 
low:     0 high:     0
Jul 20 13:45:48 server kernel: Zone:Normal freepages:  1084 min:  1279 
low:  4544 high:  6304
Jul 20 13:45:48 server kernel: Zone:HighMem freepages:386679 min:   255 
low: 61952 high: 92928
Jul 20 13:45:48 server kernel: Free pages:      389647 (386679 HighMem)
Jul 20 13:45:48 server kernel: ( Active: 2259787/488777, 
inactive_laundry: 244282, inactive_clean: 244366, free: 389647 )
Jul 20 13:45:48 server kernel:   aa:0 ac:0 id:0 il:0 ic:0 fr:1884
Jul 20 13:45:48 server kernel:   aa:1620 ac:1801 id:231 il:15 ic:0 fr:1085
Jul 20 13:45:48 server kernel:   aa:1099230 ac:1157136 id:488536 
il:244277 ic:244366 fr:386679
Jul 20 13:45:48 server kernel: 0*4kB 0*8kB 1*16kB 1*32kB 1*64kB 0*128kB 
1*256kB 0*512kB 1*1024kB 1*2048kB 1*4096kB = 7536kB)Jul 20 13:45:48 
server kernel: 55*4kB 9*8kB 19*16kB 9*32kB 0*64kB 1*128kB 1*256kB 
0*512kB 1*1024kB 1*2048kB 0*4096kB = 4340kB)
Jul 20 13:45:48 server kernel: 291229*4kB 46179*8kB 711*16kB 1*32kB 
1*64kB 1*128kB 1*256kB 1*512kB 0*1024kB 0*2048kB 0*4096kB = 1546716kB)
Jul 20 13:45:48 server kernel: Swap cache: add 192990, delete 189665, 
find 21145/90719, race 0+0
Jul 20 13:45:48 server kernel: 139345 pages of slabcache
Jul 20 13:45:48 server kernel: 1890 pages of kernel stacks
Jul 20 13:45:48 server kernel: 0 lowmem pagetables, 274854 highmem 
pagetables
Jul 20 13:45:48 server kernel: Free swap:       16749720kB
Jul 20 13:45:49 server kernel: 4194304 pages of RAM
Jul 20 13:45:49 server kernel: 3899360 pages of HIGHMEM
Jul 20 13:45:49 server kernel: 140718 reserved pages
Jul 20 13:45:49 server kernel: 35350398 pages shared
Jul 20 13:45:49 server kernel: 3325 pages swap cached

/proc/meminfo LowFree info:
LowFree:         17068 kB    ------> Do you think this value is too low?

Zone:Normal freepages:  1084 min:  1279 low:  4544 high:  6304   ---->  
(freepages < min) It's normal?
Zone:HighMem freepages:386679 min:   255 low: 61952 high: 92928  ----> 
(freepages < min) It's normal?

Thanks a lot Neil!

Márcio Oliveira.