linux-kernel - Re: [RFC PATCH 01/13] arm: Fix mutual exclusion in arch

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Message-ID: <e6b5fffd-1d40-494d-d59b-f98f3c6c9655@gmail.com>
Date:   Sat, 17 Nov 2018 16:00:39 +1300
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Finn Thain <fthain@...egraphics.com.au>,
        Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        Stephen N Chivers <schivers@....com.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 01/13] arm: Fix mutual exclusion in arch_gettimeoffset

Hi Finn,

Am 17.11.2018 um 11:49 schrieb Finn Thain:
> On Fri, 16 Nov 2018, Russell King - ARM Linux wrote:
>
>>
>> The EBSA110 is probably in a similar boat - I don't remember whether it
>> had 16MB or 32MB as the maximal amount of memory, but memory was getting
>> tight with some kernels even running a minimalist userspace.
>>
>> So, it's probably time to say goodbyte to the kernel support for these
>> platforms.
>>
>
> Your call.
>
> Note that removing code from mainline won't help users obtain older,
> smaller, -stable kernel releases, free from the bug we were discussing.
> (The bug appeared in Linux v2.6.32.)
>
> BTW, if you did want to boot Linux on a 16 MB system, you do have some
> options.
>
> https://lwn.net/Articles/741494/
> https://lwn.net/Articles/608945/
> https://tiny.wiki.kernel.org/
>
> Contributing to this kind of effort probably has value for IoT
> deployments. I suspect it also cuts a small amount of bloat from a large
> number of other Linux systems.

I boot 4.19 on a system with 14 MB RAM - 10 MB remain for user space 
once the kernel loads. After remote login, 4 MB of that remain free for 
buffers or user code (1.5 MB swapped).
That's with sysvinit - Christian tried to boot a systemd userland on his 
Falcon once, and ran out of memory before swap could be activated.

I shouldn't say 16 or 32 MB are hopeless. And the 2.6 kernels were a lot 
more sluggish to my recollection.

Cheers,

	Michael