linux-kernel - Re: [PATCH 04/10] drm/i915: Fix MAX_ORDER usage in i915_gem_object_get_pages

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Date:   Wed, 15 Mar 2023 18:28:02 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Subject: Re: [PATCH 04/10] drm/i915: Fix MAX_ORDER usage in
 i915_gem_object_get_pages_internal()

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@...el.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.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov