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    SubjectRe: [PATCH 2/6] memcg: simplify move_account() check.
    On Fri, Feb 17, 2012 at 06:26:12PM +0900, KAMEZAWA Hiroyuki wrote:
    > >From 3b6620772d7fd7b2126d5253eafb6afaf4ed6e34 Mon Sep 17 00:00:00 2001
    > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > Date: Thu, 2 Feb 2012 10:02:39 +0900
    > Subject: [PATCH 2/6] memcg: simplify move_account() check.
    >
    > In memcg, for avoiding take-lock-irq-off at accessing page_cgroup,
    > a logic, flag + rcu_read_lock(), is used. This works as following
    >
    > CPU-A CPU-B
    > rcu_read_lock()
    > set flag
    > if(flag is set)
    > take heavy lock
    > do job.
    > synchronize_rcu() rcu_read_unlock()
    > take heavy lock.
    >
    > In recent discussion, it's argued that using per-cpu value for this
    > flag just complicates the code because 'set flag' is very rare.
    >
    > This patch changes 'flag' implementation from percpu to atomic_t.
    > This will be much simpler.
    >
    > Changelog v5.
    > - removed redundant ().
    > - updated patch description.
    >
    > Changelog: v4
    > - fixed many typos.
    > - fixed return value to be bool
    > - add comments.
    > Changelog: v3
    > - this is a new patch since v3.
    >
    > Acked-by: Greg Thelen <gthelen@google.com>
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    Much better!

    Acked-by: Johannes Weiner <hannes@cmpxchg.org>


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