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Date: Tue, 4 Aug 2026 22:23:41 +0000
From: Yosry Ahmed <yosry@kernel.org>
To: Brendan Jackman <jackmanb@google.com>
Cc: Borislav Petkov <bp@alien8.de>, 
	Dave Hansen <dave.hansen@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>, 
	Andrew Morton <akpm@linux-foundation.org>, David Hildenbrand <david@kernel.org>, 
	Vlastimil Babka <vbabka@kernel.org>, Mike Rapoport <rppt@kernel.org>, Wei Xu <weixugc@google.com>, 
	Johannes Weiner <hannes@cmpxchg.org>, Zi Yan <ziy@nvidia.com>, Lorenzo Stoakes <ljs@kernel.org>, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, 
	Sumit Garg <sumit.garg@oss.qualcomm.com>, Will Deacon <will@kernel.org>, rientjes@google.com, 
	"Kalyazin, Nikita" <kalyazin@amazon.co.uk>, patrick.roy@linux.dev, "Itazuri, Takahiro" <itazur@amazon.co.uk>, 
	Andy Lutomirski <luto@kernel.org>, David Kaplan <david.kaplan@amd.com>, 
	Thomas Gleixner <tglx@kernel.org>, Patrick Bellasi <derkling@google.com>, 
	Reiji Watanabe <reijiw@google.com>, Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH v3 13/26] mm: introduce freetype_t
Message-ID: <anJmOMqCVugycC9x@google.com>
References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com>
 <20260726-page_alloc-unmapped-v3-13-6f5729aa9832@google.com>
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In-Reply-To: <20260726-page_alloc-unmapped-v3-13-6f5729aa9832@google.com>

> @@ -179,24 +180,62 @@ static inline bool migratetype_is_mergeable(int mt)
>  
>  #define for_each_free_list(list, zone, order) 				\
>  	for (order = 0; order < NR_PAGE_ORDERS; order++) 		\
> -		for (unsigned int __type = 0; 				\
> -		     __type < MIGRATE_TYPES &&				\
> -			(list = &(zone)->free_area[order].free_list[__type], 1); \
> -		     __type++)
> +		for (unsigned int __idx = 0; 				\
> +		     __idx < NR_FREETYPE_IDXS &&			\
> +			(list = &(zone)->free_area[order].free_list[__idx], 1); \
> +		     __idx++)
> +
> +static inline freetype_t migrate_to_freetype(enum migratetype mt,
> +					     unsigned int flags)
> +{
> +	freetype_t freetype;
> +
> +	/* No flags supported yet. */
> +	VM_WARN_ON_ONCE(flags);
> +
> +	freetype.migratetype = mt;
> +	return freetype;
> +}
> +
> +static inline enum migratetype free_to_migratetype(freetype_t freetype)
> +{
> +	return freetype.migratetype;
> +}
> +
> +/* Convenience helper, return the freetype modified to have the migratetype. */
> +static inline freetype_t freetype_with_migrate(freetype_t freetype,
> +					       enum migratetype migratetype)
> +{
> +	return migrate_to_freetype(migratetype, freetype_flags(freetype));
> +}
>  
>  extern int page_group_by_mobility_disabled;
>  
> +freetype_t get_pfnblock_freetype(const struct page *page, unsigned long pfn);
> +
>  #define get_pageblock_migratetype(page) \
>  	get_pfnblock_migratetype(page, page_to_pfn(page))
>  
> +#define get_pageblock_freetype(page) \
> +	get_pfnblock_freetype(page, page_to_pfn(page))
> +
>  #define folio_migratetype(folio) \
>  	get_pageblock_migratetype(&folio->page)
>  
>  struct free_area {
> -	struct list_head	free_list[MIGRATE_TYPES];
> +	struct list_head	free_list[NR_FREETYPE_IDXS];
>  	unsigned long		nr_free;
>  };
>  
> +static inline
> +struct list_head *free_area_list(struct free_area *area, freetype_t type)
> +{
> +	int idx = freetype_idx(type);
> +
> +	VM_WARN_ON(idx < 0);
> +	return &area->free_list[idx];

Should we return NULL here if idx < 0 instead of an out of bounds
access?