Re: [RFC][PATCH] OVERCOMMIT_ALWAYS extension

[Darren Hart <dvhltc@us.ibm.com>]

Badari Pulavarty wrote:
>> ...
>>I say "as far as it goes" because I don't think it's actually going to
>>achieve the effect you said you wanted in your original post.
>>
>>As you've probably noticed, switching off VM_ACCOUNT here will mean that
>>the shm object is accounted page by page as it's instantiated, and I
>>expect you're okay with that.  But you want madvise(DONTNEED) to free
>>up those reservations: it'll unmap the pages from userspace, but it
>>won't free the pages from the shm object, so the reservations will
>>still be in force, and accumulate.
> 
> 
> Darren Hart is working on patch to add madvise(DISCARD) to extend
> the functionality of madvise(DONTNEED) to really drop those pages.
> I was going to ask your opinion on that approach :) 
> 
> shmget(SHM_NORESERVE) + madvise(DISCARD) should do what I was
> hoping for. (BTW, none of this has been tested with database stuff -
> I am just concentrating on reasonable extensions.
> 
> Here is the version of patch under test. 
> (Darren - I am sending this out without your permission, I hope
> you are okay with it).
>  

Of course, no problem.  I have a separate patch for sles9sp2 if that is of 
interest.  Please keep me in the loop with any feedback on the patch.

-- 
Darren Hart
IBM Linux Technology Center
Linux Kernel Team
Phone: 503 578 3185
   T/L: 775 3185

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