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Date: Thu, 26 Feb 2026 13:37:42 -0800
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From: Shakeel Butt <shakeel.butt@linux.dev>
To: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>, 
	Sergey Senozhatsky <senozhatsky@chromium.org>, Johannes Weiner <hannes@cmpxchg.org>, 
	Jens Axboe <axboe@kernel.dk>, Yosry Ahmed <yosry.ahmed@linux.dev>, 
	Nhat Pham <hoangnhat.pham@linux.dev>, Nhat Pham <nphamcs@gmail.com>, 
	Chengming Zhou <chengming.zhou@linux.dev>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, 
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com
Subject: Re: [PATCH 3/8] mm/zsmalloc: Introduce objcgs pointer in struct
 zpdesc
Message-ID: <aaC80TsqmKpwFzQf@linux.dev>
References: <20260226192936.3190275-1-joshua.hahnjy@gmail.com>
 <20260226192936.3190275-4-joshua.hahnjy@gmail.com>
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On Thu, Feb 26, 2026 at 11:29:26AM -0800, Joshua Hahn wrote:
> --- a/mm/zpdesc.h
> +++ b/mm/zpdesc.h
> @@ -20,10 +20,12 @@
>   * @zspage:		Points to the zspage this zpdesc is a part of.
>   * @first_obj_offset:	First object offset in zsmalloc pool.
>   * @_refcount:		The number of references to this zpdesc.
> + * @objcgs:		Array of objcgs pointers that the stored objs
> + *			belong to. Overlayed on top of page->memcg_data, and
> + *			will always have first bit set if it is a valid pointer.
>   *
>   * This struct overlays struct page for now. Do not modify without a good
> - * understanding of the issues. In particular, do not expand into the overlap
> - * with memcg_data.
> + * understanding of the issues.
>   *
>   * Page flags used:
>   * * PG_private identifies the first component page.
> @@ -47,6 +49,9 @@ struct zpdesc {
>  	 */
>  	unsigned int first_obj_offset;
>  	atomic_t _refcount;
> +#ifdef CONFIG_MEMCG
> +	unsigned long objcgs;

Why not just strore struct obj_cgroup ** instead of unsigned long? You will not
need to do conversions when storing or accessing.