Subject: Re: [PATCH] Hugepages should be accounted as unevictable pages.
From: Alok Kataria <akataria@vmware.com>
Reply-To: akataria@vmware.com
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Lee Schermerhorn <Lee.Schermerhorn@hp.com>, Mel Gorman <mel@csn.ul.ie>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>
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Organization: VMware INC.
Date: Tue, 23 Jun 2009 17:08:34 -0700
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On Tue, 2009-06-23 at 16:41 -0700, Dave Hansen wrote:
> On Tue, 2009-06-23 at 15:23 -0700, Alok Kataria wrote:
> > > Could you just teach the thing to which you are hinting that it also
> > > needs to go look in sysfs for huge page counts?
> > 
> > :) yeah i could do that too...the point is that its a module and the
> > function to get the hugepages count is not exported right now. I could
> > very well add this as an exported symbol and use it from there, but
> > there can be someone who doesn't want symbols to be unnecessarily
> > exported if their is no in-tree modular usage of that symbol. 
> 
> Hmmm.  So what is the module doing?  The ol', "try to get as much memory
> as I possibly can" game? :)
> 
> It sounds like you can get access to the vm statistics from existing
> exported symbols, but the stats don't give you quite the info that you
> need.

>   So, you're trying to change things that you *can* get access to.

:) Not entirely, I thought that UNEVICTABLE by definition should
consider hugepages too. 

> 
> We do export all this stuff to userspace.  We export all of the huge
> page sizes and how many pages are reserved, used, and allocated in each,
> plus the contentious Unevictable.  Could you just do this calculation in
> userspace and pass it into the module with a modparam or sysfs file?

Hmm...lets see, I will look to moving that to userspace or something. 

But irrespective of my need, we must clear the confusion around what
unevictable should actually mean. 

I am biased towards getting hugepages accounted in that :), but what do
others think ? 

Lee, I will let you take a decision on that, if the current semantics
look okay, it would be great if you could update the unevictable_lru
documentation about this being just the number of pages on
unevictable_lru.

Thanks,
Alok
> 
> -- Dave
> 

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