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

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Message-Id: <20120314164334.5e35f3b6.akpm@linux-foundation.org>
Date:	Wed, 14 Mar 2012 16:43:34 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
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 Wed, 14 Mar 2012 15:51:50 +0530
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:

> 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 ?

If the for_each_hstate() macro took an additional arg which holds the
base address of the array, that macro could have been used here.

Or perhaps not - I didn't look too closely ;)  It isn't important.
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