linux-kernel - Re: [PATCH v5 04/14] kmem accounting basic infrastructure

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Message-Id: <20121017151207.e8bb3db2.akpm@linux-foundation.org>
Date:	Wed, 17 Oct 2012 15:12:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Tejun Heo <tj@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>, <devel@...nvz.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 04/14] kmem accounting basic infrastructure

On Tue, 16 Oct 2012 14:16:41 +0400
Glauber Costa <glommer@...allels.com> wrote:

> This patch adds the basic infrastructure for the accounting of kernel
> memory. To control that, the following files are created:
> 
>  * memory.kmem.usage_in_bytes
>  * memory.kmem.limit_in_bytes
>  * memory.kmem.failcnt

gargh.  "failcnt" is not a word.  Who was it who first thought that
omitting voewls from words improves anything?

Sigh.  That pooch is already screwed and there's nothing we can do
about it now.

>  * memory.kmem.max_usage_in_bytes
> 
> They have the same meaning of their user memory counterparts. They
> reflect the state of the "kmem" res_counter.
> 
> Per cgroup kmem memory accounting is not enabled until a limit is set
> for the group. Once the limit is set the accounting cannot be disabled
> for that group.  This means that after the patch is applied, no
> behavioral changes exists for whoever is still using memcg to control
> their memory usage, until memory.kmem.limit_in_bytes is set for the
> first time.
> 
> We always account to both user and kernel resource_counters. This
> effectively means that an independent kernel limit is in place when the
> limit is set to a lower value than the user memory. A equal or higher
> value means that the user limit will always hit first, meaning that kmem
> is effectively unlimited.
> 
> People who want to track kernel memory but not limit it, can set this
> limit to a very high number (like RESOURCE_MAX - 1page - that no one
> will ever hit, or equal to the user memory)
> 
>
> ...
>
> +/* internal only representation about the status of kmem accounting. */
> +enum {
> +	KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */
> +};
> +
> +#define KMEM_ACCOUNTED_MASK (1 << KMEM_ACCOUNTED_ACTIVE)
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +static void memcg_kmem_set_active(struct mem_cgroup *memcg)
> +{
> +	set_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted);
> +}
> +#endif

I don't think memcg_kmem_set_active() really needs to exist.  It has a
single caller and is unlikely to get any additional callers, so just
open-code it there?



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