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From:   Zi Yan <ziy@nvidia.com>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     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, Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC PATCH 12/15] mm: Make MAX_ORDER of buddy allocator configurable via Kconfig SET_MAX_ORDER.
Date:   Fri, 06 Aug 2021 11:23:40 -0400
Message-ID: <58BBA058-DAD4-42F4-9AA6-ECFC5F7D61CC@nvidia.com>
In-Reply-To: <1a5c17ac-7f63-6aae-b83b-4438bfa6fe34@suse.cz>
References: <20210805190253.2795604-1-zi.yan@sent.com>
 <20210805190253.2795604-13-zi.yan@sent.com>
 <1a5c17ac-7f63-6aae-b83b-4438bfa6fe34@suse.cz>
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On 6 Aug 2021, at 11:16, Vlastimil Babka wrote:

> On 8/5/21 9:02 PM, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>> +config SET_MAX_ORDER
>> +	int "Set maximum order of buddy allocator"
>> +    depends on SPARSEMEM_VMEMMAP && (ARCH_FORCE_MAX_ORDER =3D 0)
>> +	range 11 255
>> +	default "11"
>> +	help
>> +	  The kernel memory allocator divides physically contiguous memory
>> +	  blocks into "zones", where each zone is a power of two number of
>> +	  pages.  This option selects the largest power of two that the kern=
el
>> +	  keeps in the memory allocator.  If you need to allocate very large=

>> +	  blocks of physically contiguous memory, then you may need to
>> +	  increase this value.
>> +
>> +	  This config option is actually maximum order plus one. For example=
,
>> +	  a value of 11 means that the largest free memory block is 2^10 pag=
es.
>
> It's enough that it's confusing for the devs, we could spare the users =
and add
> +1 to the value they specify :)

Sure. I will change the existing ARCH_FORCE_MAX_ORDER too, otherwise peop=
le might
get confused by two different MAX_ORDERs. Since this Kconfig only appears=
 when
ARCH_FORCE_MAX_ORDER is not specified.


=E2=80=94
Best Regards,
Yan, Zi

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