linux-kernel - Re: [RFC][2/3] Account and control virtual address space allocations

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Date:	Mon, 17 Mar 2008 10:02:09 +0800
From:	"Paul Menage" <menage@...gle.com>
To:	"Balbir Singh" <balbir@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, "Hugh Dickins" <hugh@...itas.com>,
	"Sudhir Kumar" <skumar@...ux.vnet.ibm.com>,
	"YAMAMOTO Takashi" <yamamoto@...inux.co.jp>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	"David Rientjes" <rientjes@...gle.com>,
	"Pavel Emelianov" <xemul@...nvz.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][2/3] Account and control virtual address space allocations

On Mon, Mar 17, 2008 at 1:30 AM, Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
>   /*
>  + * Check if the current cgroup exceeds its address space limit.
>  + * Returns 0 on success and 1 on failure.
>  + */
>  +int mem_cgroup_update_as(struct mm_struct *mm, long nr_pages)
>  +{
>  +       int ret = 0;
>  +       struct mem_cgroup *mem;
>  +       if (mem_cgroup_subsys.disabled)
>  +               return ret;
>  +
>  +       rcu_read_lock();
>  +       mem = rcu_dereference(mm->mem_cgroup);
>  +       css_get(&mem->css);
>  +       rcu_read_unlock();
>  +

How about if this function avoided charging the root cgroup? You'd
save 4 atomic operations on a global data structure on every
mmap/munmap when the virtual address limit cgroup wasn't in use, which
could be significant on a large system. And I don't see situations
where you really need to limit the address space of the root cgroup.

Paul
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