linux-kernel - Re: [PATCH v1 11/19] zsmalloc: squeeze freelist into page->mapping

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Date:	Tue, 15 Mar 2016 15:40:53 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, jlayton@...chiereds.net,
	bfields@...ldses.org, Vlastimil Babka <vbabka@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, koct9i@...il.com,
	aquini@...hat.com, virtualization@...ts.linux-foundation.org,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	rknize@...orola.com, Rik van Riel <riel@...hat.com>,
	Gioh Kim <gurugio@...mail.net>
Subject: Re: [PATCH v1 11/19] zsmalloc: squeeze freelist into page->mapping

On (03/11/16 16:30), Minchan Kim wrote:
> -static void *location_to_obj(struct page *page, unsigned long obj_idx)
> +static void objidx_to_page_and_ofs(struct size_class *class,
> +				struct page *first_page,
> +				unsigned long obj_idx,
> +				struct page **obj_page,
> +				unsigned long *ofs_in_page)

this looks big; 5 params, function "returning" both page and offset...
any chance to split it in two steps, perhaps?

besides, it is more intuitive (at least to me) when 'offset'
shortened to 'offt', not 'ofs'.

	-ss

>  {
> -	unsigned long obj;
> +	int i;
> +	unsigned long ofs;
> +	struct page *cursor;
> +	int nr_page;
>  
> -	if (!page) {
> -		VM_BUG_ON(obj_idx);
> -		return NULL;
> -	}
> +	ofs = obj_idx * class->size;
> +	cursor = first_page;
> +	nr_page = ofs >> PAGE_SHIFT;
>  
> -	obj = page_to_pfn(page) << OBJ_INDEX_BITS;
> -	obj |= ((obj_idx) & OBJ_INDEX_MASK);
> -	obj <<= OBJ_TAG_BITS;
> +	*ofs_in_page = ofs & ~PAGE_MASK;
> +
> +	for (i = 0; i < nr_page; i++)
> +		cursor = get_next_page(cursor);
>  
> -	return (void *)obj;
> +	*obj_page = cursor;
>  }