linux-kernel - Re: [PATCH v2 0/3] mm: tlb swap entries batch async release

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Message-Id: <20240806153947.1af20ffccfb42f1e8d981d6f@linux-foundation.org>
Date: Tue, 6 Aug 2024 15:39:47 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Barry Song <21cnbao@...il.com>
Cc: zhiguojiang <justinjiang@...o.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>, Nick Piggin
 <npiggin@...il.com>, Peter Zijlstra <peterz@...radead.org>, Arnd Bergmann
 <arnd@...db.de>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko
 <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, Shakeel
 Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>,
 linux-arch@...r.kernel.org, cgroups@...r.kernel.org, kernel test robot
 <lkp@...el.com>, opensource.kernel@...o.com
Subject: Re: [PATCH v2 0/3] mm: tlb swap entries batch async release

On Wed, 7 Aug 2024 04:32:09 +0800 Barry Song <21cnbao@...il.com> wrote:

> > > their independent mm, rather than parent and child processes share the
> > > same mm. Therefore, when the kernel executes multiple exiting process
> > > simultaneously, they will definitely occupy multiple CPU core resources
> > > to complete it.
> >
> > What I'm asking is why not change those userspace processes so that they
> > fork off a child process which shares the MM (shared mm_struct) and
> > then the original process exits, leaving the asynchronously-running
> > child to clean up the MM resources.
> 
> Not Zhiguo. From my perspective as a phone engineer, this issue isn't related
> to the parent-child process or the wait() function. Phones rely heavily on
> mechanisms similar to the OOM killer to function efficiently. For instance,
> if you're using apps like YouTube, TikTok, and Facebook, and then you
> open the camera app to take a photo, the camera app becomes the foreground
> process and demands a lot of memory. In this scenario, the phone might
> decide to terminate the most memory-consuming and less important apps,
> such as TikTok or YouTube, to free up memory for the camera app. TikTok
> and YouTube become less important because they are no longer occupying
> the phone's screen and have moved to the background. The faster TikTok
> and YouTube can be unmapped, the quicker the camera app can launch,
> enhancing the user experience.

I don't see how this relates to my question.

Userspace can arrange for these resources to be released in an
asynchronous fashion (can't it?).  So why change the kernel to do that?