Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 6 Aug 2021 13:27:27 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Zi Yan <ziy@nvidia.com>
cc:     Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        Matthew Wilcox <willy@infradead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Michal Hocko <mhocko@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot
 time parameter.
In-Reply-To: <F34DBD0A-22DE-4CF2-B784-BBDD80A8E85A@nvidia.com>
Message-ID: <6ae6cd92-3ff4-7ed3-b337-a4dfe33da1c@google.com>
References: <20210805190253.2795604-1-zi.yan@sent.com> <0d374eed-cc52-a656-b338-1156782bdf7e@suse.cz> <F34DBD0A-22DE-4CF2-B784-BBDD80A8E85A@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

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