linux-kernel - Re: [-mm][PATCH 4/4] Add memrlimit controller accounting and control (v5)

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Date:	Wed, 21 May 2008 21:24:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, Pavel Emelianov <xemul@...nvz.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [-mm][PATCH 4/4] Add memrlimit controller accounting and
 control (v5)

On Wed, 21 May 2008 21:00:12 +0530 Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> 
> This patch adds support for accounting and control of virtual address space
> limits. The accounting is done via the rlimit_cgroup_(un)charge_as functions.
> The core of the accounting takes place during fork time in copy_process(),
> may_expand_vm(), remove_vma_list() and exit_mmap(). 
> 
> Changelog v5->v4
> 
> Move specific hooks in code to insert_vm_struct
> Use mmap_sem to protect mm->owner from changing and mm->owner from
> changing cgroups.
> 
> ...
>
> + * brk(), sbrk()), stack expansion, mremap(), etc - called with
> + * mmap_sem held.
> + * decreasing - called with mmap_sem held.
> + * This callback is called with mmap_sem held

It's good to document the locking prerequisites but for rwsems, one
should specify whether it must be held for reading or for writing.

Of course, down_write() is a superset of down_read(), so if it's "held
for reading" then either mode-of-holding is OK.  But it's best to spell
all that out.

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