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Subject: Re: [PATCH] mm: Free per cpu pages async to shorten program exit time
To:     Michal Hocko <mhocko@suse.com>
Cc:     ultrachin@163.com, akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, brookxu.cn@gmail.com,
        chen xiaoguang <xiaoggchen@tencent.com>,
        zeng jingxiang <linuszeng@tencent.com>,
        lu yihui <yihuilu@tencent.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>
References: <20211008063933.331989-1-ultrachin@163.com>
 <d71e6021-777b-3ca9-b08f-64fe7ff51e08@redhat.com>
 <YWQDqtnA5FXk7xan@dhcp22.suse.cz>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <278a6cda-3095-5e27-e136-2765f73bc67d@redhat.com>
Date:   Mon, 11 Oct 2021 11:40:12 +0200
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On 11.10.21 11:28, Michal Hocko wrote:
> On Fri 08-10-21 10:17:50, David Hildenbrand wrote:
>> On 08.10.21 08:39, ultrachin@163.com wrote:
>>> From: chen xiaoguang <xiaoggchen@tencent.com>
>>>
>>> The exit time is long when program allocated big memory and
>>> the most time consuming part is free memory which takes 99.9%
>>> of the total exit time. By using async free we can save 25% of
>>> exit time.
>>>
>>> Signed-off-by: chen xiaoguang <xiaoggchen@tencent.com>
>>> Signed-off-by: zeng jingxiang <linuszeng@tencent.com>
>>> Signed-off-by: lu yihui <yihuilu@tencent.com>
>>
>> I recently discussed with Claudio if it would be possible to tear down the
>> process MM deferred, because for some use cases (secure/encrypted
>> virtualization, very large mmaps) tearing down the page tables is already
>> the much more expensive operation.
>>
>> There is mmdrop_async(), and I wondered if one could reuse that concept when
>> tearing down a process -- I didn't look into feasibility, however, so it's
>> just some very rough idea.
> 
> This is not a new problem. Large process tear down can take ages. The
> primary road block has been accounting. This lot of work has to be
> accounted to the proper domain (e.g. cpu cgroup). 

In general, yes. For some setups where admins don't care about that 
accounting (e.g., enabled via some magic toggle for large VMs), I guess 
this accounting isn't the major roadblock, correct?

-- 
Thanks,

David / dhildenb