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Date: Tue, 13 Nov 2018 18:27:05 +0100
From: Oleksandr Natalenko <oleksandr@natalenko.name>
Subject: Re: [PATCH V3] KSM: allow dedup all tasks memory
In-Reply-To: <CAGqmi77Ok0usUt5gfyPMYx22FdgqntSrwiap7=DT81HZuvNm_Q@mail.gmail.com>
References: <d45addefdf05b84af96fb494d52b4ec4@natalenko.name>
 <CAGqmi77Ok0usUt5gfyPMYx22FdgqntSrwiap7=DT81HZuvNm_Q@mail.gmail.com>
Message-ID: <5a9ef9a0c8ed688e1566fc7380915837@natalenko.name>
Sender: owner-linux-mm@kvack.org
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To: Timofey Titovets <timofey.titovets@synesis.ru>
Cc: linux-doc@vger.kernel.org, Linux Kernel <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, Matthew Wilcox <willy@infradead.org>

On 13.11.2018 18:10, Timofey Titovets wrote:
> You mean try do something, like that right?
> 
> read_lock(&tasklist_lock);
>   <get reference to task>
>   task_lock(task);
> read_unlock(&tasklist_lock);
>     last_pid = task_pid_nr(task);
>     ksm_import_task_vma(task);
>   task_unlock(task);

No, task_lock() uses spin_lock() under the bonnet, so this will be the 
same.

Since the sole reason you have to lock/acquire/get a reference to 
task_struct here is to prevent it from disappearing, I was thinking 
about using get_task_struct(), which just increases atomic 
task_struct.usage value (IOW, takes a reference). I *hope* this will be 
enough to prevent task_struct from disappearing in the meantime.

Someone, correct me if I'm wrong.

-- 
   Oleksandr Natalenko (post-factum)