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From:   Matthew Wilcox <willy@infradead.org>
To:     Matteo Croce <mcroce@linux.microsoft.com>
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Subject: Re: [PATCH net-next v5 1/5] mm: add a signature in struct page
Message-ID: <YJ3Lrdx1oIm/MDV8@casper.infradead.org>
References: <20210513165846.23722-1-mcroce@linux.microsoft.com>
 <20210513165846.23722-2-mcroce@linux.microsoft.com>
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On Thu, May 13, 2021 at 06:58:42PM +0200, Matteo Croce wrote:
>  		struct {	/* page_pool used by netstack */
> +			/**
> +			 * @pp_magic: magic value to avoid recycling non
> +			 * page_pool allocated pages.
> +			 * It aliases with page->lru.next

I'm not really keen on documenting what aliases with what.
pp_magic also aliases with compound_head, 'next' (for slab),
and dev_pagemap.  This is an O(n^2) documentation problem ...

I feel like I want to document the pfmemalloc bit in mm_types.h,
but I don't have a concrete suggestion yet.

> +++ b/include/net/page_pool.h
> @@ -63,6 +63,8 @@
>   */
>  #define PP_ALLOC_CACHE_SIZE	128
>  #define PP_ALLOC_CACHE_REFILL	64
> +#define PP_SIGNATURE		(POISON_POINTER_DELTA + 0x40)

I wonder if this wouldn't be better in linux/poison.h?