Re: Finding kernel RAM consumers ?

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Matthew Wilcox <willy@infradead.org>,
	Joakim Tjernlund <Joakim.Tjernlund@infinera.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Finding kernel RAM consumers ?
Date: Tue, 7 Jun 2022 10:44:12 +0100	[thread overview]
Message-ID: <Yp8d7NZ561/yr0HF@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAK8P3a2GkOJbM_ssRJ5pQtcaLn6pP3zZHgeH7CQ_RsPSKQVD6g@mail.gmail.com>

On Tue, Jun 07, 2022 at 10:38:54AM +0200, Arnd Bergmann wrote:
> On Tue, Jun 7, 2022 at 7:41 AM Alexander Dahl <ada@thorsis.com> wrote:
> > Am Fri, Jun 03, 2022 at 08:11:31PM +0200 schrieb Arnd Bergmann:
> > > On Fri, Jun 3, 2022 at 7:29 PM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > I think this is a case of "patches welcome". Nobody has really needed
> > > this so far, but as even the smaller machines are slowly migrating from
> > > 32-bit to 64-bit cores, optimizing this will get interesting for more
> > >  developers. There are probably other low-hanging
> > > fruit that you can address after figuring out.
> >
> > The SiP variants of at91 SAMA5D2 (armv7) or SAM9x60 (armv5) come with
> > 64 MiB or 128 MiB, and given the latter is a new SoC announced only
> > two or three years ago, requiring at least 256 MiB would be at best
> > unfortunate.  Given those SoCs are used in industrial applications
> > with very long support times, I think 32bit ARM will stay for years,
> > even with new products.
> 
> Yes, of course, and there is nothing wrong with that. We already see
> Cortex-A7 cores down to 7nm, all running Linux, and I expect there
> will likely be another 5 to 10 years of new 32-bit chips, and then another
> 10 years of people putting the existing chips into production, and after
> that a slow decline of users updating their kernels before supporting
> 32-bit hardware becomes too expensive to support in the kernel.

It should be noted that 20 years puts us past the 2038 32-bit time_t
wrap problem - and although there's been work to address that in the
UAPI, that doesn't mean that userspace will cope.

Anyone deploying a system that is expected to still be live beyond
the end of 32-bit time_t had better be testing their userspace for
that event now!

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel