linux-kernel - Re: [PATCH -V3 2/8] memcg: Add HugeTLB extension

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Date:	Wed, 14 Mar 2012 15:51:50 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, mgorman@...e.de,
	kamezawa.hiroyu@...fujitsu.com, dhillf@...il.com,
	aarcange@...hat.com, mhocko@...e.cz, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH -V3 2/8] memcg: Add HugeTLB extension

On Tue, 13 Mar 2012 14:33:16 -0700, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Tue, 13 Mar 2012 12:37:06 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> 
> > +static int mem_cgroup_hugetlb_usage(struct mem_cgroup *memcg)
> > +{
> > +	int idx;
> > +	for (idx = 0; idx < hugetlb_max_hstate; idx++) {
> > +		if (memcg->hugepage[idx].usage > 0)
> > +			return memcg->hugepage[idx].usage;
> > +	}
> > +	return 0;
> > +}
> 
> Please document the function?  Had you done this, I might have been
> able to work out why the function bales out on the first used hugepage
> size, but I can't :(

I guess the function is named wrongly. I will rename it to
mem_cgroup_have_hugetlb_usage() in the next iteration ? The function
will return (bool) 1 if it has any hugetlb resource usage.

> 
> This could have used for_each_hstate(), had that macro been better
> designed (or updated).
> 

Can you explain this ?. for_each_hstate allows to iterate over
different hstates. But here we need to look at different hugepage
rescounter in memcg. I can still use for_each_hstate() and find the
hstate index (h - hstates) and use that to index memcg rescounter
array. But that would make it more complex ?

> Upon return this function coerces an unsigned long long into an "int". 
> We decided last week that more than 2^32 hugepages was not
> inconceivable, so I guess that's a bug.
> 

-aneesh

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