Re: Question about hugepages, shared memory, and /dev/shm....

  • From: Ls Cheng <exriscer@xxxxxxxxx>
  • To: Mark Bobak <Mark.Bobak@xxxxxxxxxxxx>
  • Date: Wed, 16 Apr 2014 19:38:40 +0200

Hi

I have seen those files in Solaris but in /tmp. It wass generated by JIT,
Java In Time Compiler in my case, not sure if it applies in your case.
Seems like it can be PL/SQL native compiled as well, since your are using
EBS it might be the case? It has nothing to do with AMM or ASMM

But look these notes

/dev/shm Filled Up With Files In Format JOXSHM_EXT_xxx_SID_xxx (Doc ID
752899.1)

Stale Native Code Files Are Being Cached with File Names Such as:
JOXSHM_EXT*, PESHM_EXT*, PESLD* or SHMDJOXSHM_EXT* (Doc ID 1120143.1)
Ora-7445 [Ioc_pin_shared_executable_object()] (Doc ID 1316906.1)

Regards

On Wed, Apr 16, 2014 at 5:47 PM, Mark Bobak <Mark.Bobak@xxxxxxxxxxxx> wrote:

>  Hi All,
>
>  So, I thought I really understood this stuff, but I’m a little baffled
> here, and I wonder if anyone can offer me a clue?
>
>  Here’s what I (think I) know:
> 1.)  AMM (setting memory_target) is *not* compatible with a hugepages
> configuration.  Any attempt to use hugepages will lock out the memory
> allocated to hugepages and AMM will only use non-hugepage memory
> allocations, the effect of which would be like removing the huge page
> allocated memory from the system.
> 2.)  ASMM (setting sga_target and pga_aggregate_target) and MMM (manually
> setting db_cache_size and pool sizes) *are* compatible with a hugepages
> configuration, and for any non-trivially sized SGA, hugepages is strongly
> recommended.
> 3.)  If hugepages are *not* configured, and AMM is used, memory segments
> will be mapped in /dev/shm.
> 4.)  If hugepages *are* used, no memory segments will be visible in
> /dev/shm.
>
>  So, that’s what I think is true about memory configuration and hugepages
> configuration.
>
>  That seems to be consistent throughout our environment, which mostly has
> ASMM or MMM and hugepages configuration.
>
>  However, and this is where my confusion comes in, we have several eBS
> environments, which seem to have a valid and active hugepages
> configuration, are using ASMM (not AMM), and *still* I can see memory
> segments allocated in /dev/shm??  Any idea how this is possible?
>
>  Here’s an example from our preprod environment:
>  (Content was too long for Oracle-L, so here’s a paste bin URL)
>
>  http://pastebin.com/7w2V2jEa
>
>   So, I’m a little baffled here.  I thought these were mutually exclusive
> features.
>
>
>  Note also that the timestamps on the /dev/shm segments is *after*
> instance startup time, so, I don’t think these are “orphan” memory
> segments….
>
>
>  Anyone out there can clue me in?
>
>
>  Thanks,
>
>
>  -Mark
>

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