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Date:   Thu, 28 Sep 2023 09:50:07 +0200 (CEST)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        David Hildenbrand <david@redhat.com>, quic_jhugo@quicinc.com,
        snitzer@kernel.org, dm <dm-devel@redhat.com>, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/10] Fix confusion around MAX_ORDER
In-Reply-To: <3c25ec6f-cd33-9445-a76f-6ec2c30755f5@redhat.com>
Message-ID: <86e7f97a-ac6b-873d-93b2-1121a464989a@redhat.com>
References: <20230315113133.11326-1-kirill.shutemov@linux.intel.com> <3c25ec6f-cd33-9445-a76f-6ec2c30755f5@redhat.com>
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On Wed, 27 Sep 2023, Paolo Bonzini wrote:

> On 3/15/23 12:31, Kirill A. Shutemov wrote:
> > MAX_ORDER currently defined as number of orders page allocator supports:
> > user can ask buddy allocator for page order between 0 and MAX_ORDER-1.
> > 
> > This definition is counter-intuitive and lead to number of bugs all over
> > the kernel.
> > 
> > Fix the bugs and then change the definition of MAX_ORDER to be
> > inclusive: the range of orders user can ask from buddy allocator is
> > 0..MAX_ORDER now.

I think that exclusive MAX_ORDER is more intuitive in the C language - 
i.e. if you write "for (i = 0; i < MAX_ORDER; i++)", you are supposed to 
loop over all allowed values. If you declare an array "void 
*array[MAX_ORDER];" you are supposed to hold a value for each allowed 
order.

Pascal has for loops and array dimensions with inclusive ranges - and it 
is more prone to off-by-one errors.

Mikulas