Message-ID: <4be7cbc0-dab5-eecc-1cea-8a6ffb831f10@linux.intel.com>
Date:   Thu, 16 Mar 2023 08:55:59 +0000
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.8.0
Subject: Re: [PATCH 04/10] drm/i915: Fix MAX_ORDER usage in
 i915_gem_object_get_pages_internal()
Content-Language: en-US
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
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>, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>
References: <20230315113133.11326-1-kirill.shutemov@linux.intel.com>
 <20230315113133.11326-5-kirill.shutemov@linux.intel.com>
 <7fe9a4a0-9b30-38db-e739-1dc1f7a8f74e@linux.intel.com>
 <20230315152802.gr2olzji5zhu6vdo@box>
 <f2f35037-d662-19c4-722a-02ec10f86f85@linux.intel.com>
 <20230315153855.aeqyxncf3k6yqipl@box>
From:   Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Organization: Intel Corporation UK Plc
In-Reply-To: <20230315153855.aeqyxncf3k6yqipl@box>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 15/03/2023 15:38, Kirill A. Shutemov wrote:
> On Wed, Mar 15, 2023 at 03:35:23PM +0000, Tvrtko Ursulin wrote:
>>
>> On 15/03/2023 15:28, Kirill A. Shutemov wrote:
>>> On Wed, Mar 15, 2023 at 02:18:52PM +0000, Tvrtko Ursulin wrote:
>>>>
>>>> On 15/03/2023 11:31, Kirill A. Shutemov wrote:
>>>>> MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
>>>>> can deliver is MAX_ORDER-1.
>>>>
>>>> This looks to be true on inspection:
>>>>
>>>> __alloc_pages():
>>>> ..
>>>> 	if (WARN_ON_ONCE_GFP(order >= MAX_ORDER, gfp))
>>>>
>>>> So a bit of a misleading name "max".. For the i915 patch:
>>>>
>>>> Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>
>>>> I don't however see the whole series to understand the context, or how you
>>>> want to handle the individual patches. Is it a tree wide cleanup of the same
>>>> mistake?
>>>
>>> The whole patchset can be seen here:
>>>
>>> https://lore.kernel.org/all/20230315113133.11326-1-kirill.shutemov@linux.intel.com/
>>>
>>> The idea is to fix all MAX_ORDER bugs first and then re-define MAX_ORDER
>>> more sensibly.
>>
>> Sounds good.
>>
>> Would you like i915 to take this patch or you will be bringing the whole lot
>> via some other route? Former is okay and latter should also be fine for i915
>> since I don't envisage any conflicts here.
> 
> I think would be better to get it via mm tree.

Ack for that. But as I saw that by the end of the series you also change 
this back as you redefine MAX_ORDER to be inclusive you could even 
simplify things and just not do anything for i915. I am pretty sure we 
never call this helper for > 4M allocations otherwise we would have seen 
this warn.

Regards,

Tvrtko