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Date:   Wed, 19 Jul 2023 16:26:04 -0600
From:   Ross Zwisler <zwisler@google.com>
To:     Mike Rapoport <rppt@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>
Subject: Re: collision between ZONE_MOVABLE and memblock allocations
Message-ID: <20230719222604.GB3528218@google.com>
References: <20230718220106.GA3117638@google.com>
 <20230719054434.GG1901145@kernel.org>
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On Wed, Jul 19, 2023 at 08:44:34AM +0300, Mike Rapoport wrote:
> 3. Switch memblock to use bottom up allocations. Historically memblock
> allocated memory from the top to avoid corrupting the kernel image and to
> avoid exhausting precious ZONE_DMA. I believe we can use bottom-up
> allocations with lower limit of memblock allocations set to 16M.
> 
> With the hack below no memblock allocations will end up in ZONE_MOVABLE:

Yep, I've confirmed that for my use cases at least this does the trick, thank
you!  I had thought about moving the memblock allocations, but had no idea it
was (basically) already supported and thought it'd be much riskier than just
adjusting where ZONE_MOVABLE lived.

Is there a reason for this to not be a real option for users, maybe per a
kernel config knob or something?  I'm happy to explore other options in this
thread, but this is doing the trick so far.