linux-kernel - Re: [patch 2/2] mm: memcontrol: default hierarchy interface for memory

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Date:	Wed, 14 Jan 2015 17:17:47 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Greg Thelen <gthelen@...gle.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] mm: memcontrol: default hierarchy interface for
 memory

I have overlooked the `none' setting...

On Thu 08-01-15 23:15:04, Johannes Weiner wrote:
[...]
> +static int memory_low_show(struct seq_file *m, void *v)
> +{
> +	struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
> +	unsigned long low = ACCESS_ONCE(memcg->low);
> +
> +	if (low == 0)
> +		seq_printf(m, "none\n");
> +	else
> +		seq_printf(m, "%llu\n", (u64)low * PAGE_SIZE);
> +
> +	return 0;
> +}

This is really confusing. What if somebody wants to protect a group
from being reclaimed? One possible and natural way would by copying
memory.max value but then `none' means something else completely.

Besides that why to call 0, which has a clear meaning, any other name?

Now that I think about the naming `none' doesn't sound that great for
max resp. high either. If for nothing else then for the above copy
example (who knows what shows up later). Sure, a huge number is bad
as well for reasons you have mentioned in other email. `resource_max'
sounds like a better fit to me. But I am lame at naming.
-- 
Michal Hocko
SUSE Labs
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