Re: [PATCH 1/1] mm: introduce process_reap system call

From: David Hildenbrand <david@redhat.com>
To: Christian Brauner <christian.brauner@ubuntu.com>,
	Suren Baghdasaryan <surenb@google.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@kernel.org>, Michal Hocko <mhocko@suse.com>,
	David Rientjes <rientjes@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
	Minchan Kim <minchan@kernel.org>,
	Christian Brauner <christian@brauner.io>,
	Christoph Hellwig <hch@infradead.org>,
	Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	Tim Murray <timmurray@google.com>,
	Linux API <linux-api@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH 1/1] mm: introduce process_reap system call
Date: Mon, 5 Jul 2021 09:41:54 +0200	[thread overview]
Message-ID: <af8e76f1-6625-25d1-98d2-a3c8a9bf2fd6@redhat.com> (raw)
In-Reply-To: <20210702152724.7fv5tnik4qlap6do@wittgenstein>

On 02.07.21 17:27, Christian Brauner wrote:
> On Thu, Jul 01, 2021 at 03:59:48PM -0700, Suren Baghdasaryan wrote:
>> On Wed, Jun 30, 2021 at 5:44 PM Andy Lutomirski <luto@kernel.org> wrote:
>>>
>>> On Wed, Jun 30, 2021 at 2:45 PM Johannes Weiner <hannes@cmpxchg.org> wrote:
>>>>
>>>> On Wed, Jun 30, 2021 at 11:51:36AM -0700, Suren Baghdasaryan wrote:
>>>>> On Wed, Jun 30, 2021 at 11:26 AM Andy Lutomirski <luto@kernel.org> wrote:
>>>>>> Also, please consider removing all mention of the word "reap" from the
>>>>>> user API.  For better or for worse, "reap" in UNIX refers to what
>>>>>> happens when a dead task gets wait()ed.  I sincerely wish I could go
>>>>>> back in time and gently encourage whomever invented that particular
>>>>>> abomination to change their mind, but my time machine doesn't work.
>>>>>
>>>>> I see. Thanks for the note. How about process_mem_release() and
>>>>> replacing reap with release everywhere?
>>>>
>>>> I don't quite understand the objection. This syscall works on tasks
>>>> that are at the end of their life, right? Isn't something like
>>>> process_mreap() establishing exactly the mental link we want here?
>>>> Release is less descriptive for what this thing is to be used for.
>>>
>>> For better or for worse, "reap" means to make a zombie pid go away.
>>>  From the description, this new operation takes a dying process (not
>>> necessarily a zombie yet) and aggressively frees its memory.  This is
>>> a different optioneration.
>>>
>>> How about "free_dying_process_memory"?
>>
>> process_mreap sounds definitely better and in line with names like
>> process_madvise. So maybe we can use it?
> 
> That one was my favorite from the list I gave too but maybe we can
> satisfy Andy too if we use one of:
> - process_mfree()
> - process_mrelease()
> 

FWIW, I tend to like process_mrelease(), due to the implied "release" 
("free the memory if there are no other references") semantics. Further, 
a new syscall feels cleaner than some magic sysfs/procfs toggle. Just my 
2 cents.

-- 
Thanks,

David / dhildenb