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

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Message-ID: <7fe9a4a0-9b30-38db-e739-1dc1f7a8f74e@linux.intel.com>
Date:   Wed, 15 Mar 2023 14:18:52 +0000
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     "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>
Cc:     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 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?

Regards,

Tvrtko

> Fix MAX_ORDER usage in i915_gem_object_get_pages_internal().
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Jani Nikula <jani.nikula@...ux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_internal.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_internal.c b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
> index 6bc26b4b06b8..eae9e9f6d3bf 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_internal.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_internal.c
> @@ -36,7 +36,7 @@ static int i915_gem_object_get_pages_internal(struct drm_i915_gem_object *obj)
>   	struct sg_table *st;
>   	struct scatterlist *sg;
>   	unsigned int npages; /* restricted by sg_alloc_table */
> -	int max_order = MAX_ORDER;
> +	int max_order = MAX_ORDER - 1;
>   	unsigned int max_segment;
>   	gfp_t gfp;
>