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

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Date:   Fri, 6 Aug 2021 13:27:27 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Zi Yan <ziy@...dia.com>
cc:     Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        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
Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot
 time parameter.

On Fri, 6 Aug 2021, Zi Yan wrote:
> 
> In addition, I would like to share more detail on my plan on supporting 1GB PUD THP.
> This patchset is the first step, enabling kernel to allocate 1GB pages, so that
> user can get 1GB THPs from ZONE_NORMAL and ZONE_MOVABLE without using
> alloc_contig_pages() or CMA allocator. The next step is to improve kernel memory
> fragmentation handling for pages up to MAX_ORDER, since currently pageblock size
> is still limited by memory section size. As a result, I will explore solutions
> like having additional larger pageblocks (up to MAX_ORDER) to counter memory
> fragmentation. I will discover what else needs to be solved as I gradually improve
> 1GB PUD THP support.

Sorry to be blunt, but let me state my opinion: 2MB THPs have given and
continue to give us more than enough trouble.  Complicating the kernel's
mm further, just to allow 1GB THPs, seems a very bad tradeoff to me.  I
understand that it's an appealing personal project; but for the sake of
of all the rest of us, please leave 1GB huge pages to hugetlbfs (until
the day when we are all using 2MB base pages).

Hugh