linux-kernel - Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time parameter.

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Message-ID: <40982106-0eee-4e62-7ce0-c4787b0afac4@suse.cz>
Date:   Fri, 6 Aug 2021 17:36:18 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Zi Yan <ziy@...dia.com>, David Hildenbrand <david@...hat.com>,
        linux-mm@...ck.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time
 parameter.

On 8/5/21 9:02 PM, Zi Yan wrote:
> From: Zi Yan <ziy@...dia.com>

> Patch 3 restores the pfn_valid_within() check when buddy allocator can merge
> pages across memory sections. The check was removed when ARM64 gets rid of holes
> in zones, but holes can appear in zones again after this patchset.

To me that's most unwelcome resurrection. I kinda missed it was going away and
now I can't even rejoice? I assume the systems that will be bumping max_order
have a lot of memory. Are they going to have many holes? What if we just
sacrificed the memory that would have a hole and don't add it to buddy at all?