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Date:   Thu, 20 Jul 2023 16:47:26 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc:     Minchan Kim <minchan@kernel.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Matthew Wilcox <willy@infradead.org>,
        Mike Rapoport <rppt@kernel.org>
Subject: Re: [RFC PATCH v2 01/21] mm/zsmalloc: create new struct zsdesc
Message-ID: <20230720074726.GF955071@google.com>
References: <20230713042037.980211-1-42.hyeyoo@gmail.com>
 <20230713042037.980211-2-42.hyeyoo@gmail.com>
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On (23/07/13 13:20), Hyeonggon Yoo wrote:
>  /*
> @@ -264,6 +247,52 @@ struct mapping_area {
>  	enum zs_mapmode vm_mm; /* mapping mode */
>  };
>  

struct zspage already has a zsdesc member at this point, so I'd prefer
to move struct zsdesc definition before struct zspage.

> +/*
> + * struct zsdesc - memory descriptor for zsmalloc memory
> + *
> + * This struct overlays struct page for now. Do not modify without a
> + * good understanding of the issues.
> + *
> + * Usage of struct page flags on zsdesc:
> + *	PG_private: identifies the first component zsdesc
> + */
> +struct zsdesc {
> +	unsigned long flags;
> +
> +	/*
> +	 * Although not used by zsmalloc, this field is used by non-LRU page migration
> +	 * code. Leave it unused.
> +	 */
> +	struct list_head lru;
> +
> +	/* Always points to zsmalloc_mops with PAGE_MAPPING_MOVABLE set */
> +	struct movable_operations *mops;
> +
> +	union {
> +		/* linked list of all zsdescs in a zspage */
> +		struct zsdesc *next;
> +		/* for huge zspages */
> +		unsigned long handle;
> +	};
> +	struct zspage *zspage;
> +	unsigned int first_obj_offset;
> +	unsigned int _refcount;
> +};
> +
> +#define ZSDESC_MATCH(pg, zs) \
> +	static_assert(offsetof(struct page, pg) == offsetof(struct zsdesc, zs))
> +
> +ZSDESC_MATCH(flags, flags);
> +ZSDESC_MATCH(lru, lru);
> +ZSDESC_MATCH(mapping, mops);
> +ZSDESC_MATCH(index, next);
> +ZSDESC_MATCH(index, handle);
> +ZSDESC_MATCH(private, zspage);
> +ZSDESC_MATCH(page_type, first_obj_offset);
> +ZSDESC_MATCH(_refcount, _refcount);
> +#undef ZSDESC_MATCH
> +static_assert(sizeof(struct zsdesc) <= sizeof(struct page));
> +
>  /* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
>  static void SetZsHugePage(struct zspage *zspage)
>  {
> -- 
> 2.41.0
>