linux-kernel - Re: [PATCH -V6 07/14] memcg: Add HugeTLB extension

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Date:	Sat, 16 Jun 2012 13:26:51 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Aditya Kali <adityakali@...gle.com>
cc:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, mgorman@...e.de, dhillf@...il.com,
	aarcange@...hat.com, mhocko@...e.cz, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH -V6 07/14] memcg: Add HugeTLB extension

On Fri, 15 Jun 2012, Aditya Kali wrote:

> Based on the usecase at Google, I see a definite value in including
> hugepage usage in memory.usage_in_bytes as well and having a single
> limit for memory usage for the job. Our jobs wants to specify only one
> (total) memory limit (including slab usage, and other kernel memory
> usage, hugepages, etc.).
> 
> The hugepage/smallpage requirements of the job vary during its
> lifetime. Having two different limits means less flexibility for jobs
> as they now have to specify their limit as (max_hugepage,
> max_smallpage) instead of max(hugepage + smallpage). Two limits
> complicates the API for the users and requires them to over-specify
> the resources.
> 

If a large number of hugepages, for example, are allocated on the command 
line because there's a lower success rate of dynamic allocation due to 
fragmentation, with your suggestion it would no longer allow the admin to 
restrict the use of those hugepages to only a particular set of tasks.  
Consider especially 1GB hugepagez on x86, your suggestion would treat a 
single 1GB hugepage which cannot be freed after boot exactly the same as 
using 1GB of memory which is obviously not the desired behavior of any 
hugetlb controller.
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