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Date:   Tue, 11 Feb 2020 19:58:12 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Rik van Riel <riel@surriel.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Chinner <david@fromorbit.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>,
        Al Viro <viro@zeniv.linux.org.uk>, kernel-team@fb.com
Subject: Re: [PATCH] vfs: keep inodes with page cache off the inode shrinker
 LRU
Message-ID: <20200212035812.GB7778@bombadil.infradead.org>
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 <20200211193101.GA178975@cmpxchg.org>
 <20200211154438.14ef129db412574c5576facf@linux-foundation.org>
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On Tue, Feb 11, 2020 at 04:28:39PM -0800, Linus Torvalds wrote:
> On Tue, Feb 11, 2020 at 3:44 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> > Testing this will be a challenge, but the issue was real - a 7GB
> > highmem machine isn't crazy and I expect the inode has become larger
> > since those days.
> 
> Hmm. I would say that in the intening years a 7GB highmem machine has
> indeed become crazy.
> 
> It used to be something we kind of supported.
> 
> But we really should consider HIGHMEM to be something that is on the
> deprecation list. In this day and age, there is no excuse for running
> a 32-bit kernel with lots of physical memory.
> 
> And if you really want to do that, and have some legacy hardware with
> a legacy use case, maybe you should be using a legacy kernel.
> 
> I'd personally be perfectly happy to start removing HIGHMEM support again.

Do we have a use case where people want to run modern 32-bit guest kernels
with more than 896MB of memory to support some horrendous legacy app?
Or is our 32-bit compat story good enough that nobody actually does this?
(Contrariwise, maybe those people are also fine with running a ten year
old kernel because a `uname -r` starting with '3' breaks said app)