Message-ID: <50A2F9FC.5050303@huawei.com>
Date: Wed, 14 Nov 2012 09:55:08 +0800
From: Li Zefan <lizefan@huawei.com>
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To: Michal Hocko <mhocko@suse.cz>
CC: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Ying Han <yinghan@google.com>,
        Tejun Heo <htejun@gmail.com>, Glauber Costa <glommer@parallels.com>
Subject: Re: [RFC] rework mem_cgroup iterator
References: <1352820639-13521-1-git-send-email-mhocko@suse.cz>
In-Reply-To: <1352820639-13521-1-git-send-email-mhocko@suse.cz>
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On 2012/11/13 23:30, Michal Hocko wrote:
> Hi all,
> this patch set tries to make mem_cgroup_iter saner in the way how it
> walks hierarchies. css->id based traversal is far from being ideal as it
> is not deterministic because it depends on the creation ordering.
> 
> Diffstat looks promising but it is fair the say that the biggest cleanup is
> just css_get_next removal. The memcg code has grown a bit but I think it is
> worth the resulting outcome (the sanity ;)).
> 

So memcg won't use css id at all, right? Then we can remove the whole css_id
stuff, and that's quite a bunch of code.

> The first patch fixes a potential misbehaving which I haven't seen but the
> fix is needed for the later patches anyway. We could take it alone as well
> but I do not have any bug report to base the fix on.
> 
> The second patch replaces css_get_next by cgroup iterators which are
> scheduled for 3.8 in Tejun's tree and I depend on the following two patches:
> fe1e904c cgroup: implement generic child / descendant walk macros
> 7e187c6c cgroup: use rculist ops for cgroup->children
> 
> The third patch is an attempt for simplification of the mem_cgroup_iter. It
> basically removes all css usages to make the code easier. The next patch
> removes the big while(!memcg) loop around the iterating logic. It could have
> been folded into #3 but I rather have the rework separate from the code
> moving noise.
> 
> The last patch just removes css_get_next as there is no user for it any
> longer.
> 
> I am also thinking that leaf-to-root iteration makes more sense but this
> patch is not included in the series yet because I have to think some
> more about the justification.
> 
> So far I didn't get to testing but I am posting this early if everybody is
> OK with this change.
> 

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