linux-kernel - Re: [PATCHv2 1/4] zsmalloc: rework zspage chain size selection

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Date:   Fri, 13 Jan 2023 09:32:21 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 1/4] zsmalloc: rework zspage chain size selection

On Mon, Jan 09, 2023 at 12:38:35PM +0900, Sergey Senozhatsky wrote:
> Computers are bad at division. We currently decide the best
> zspage chain size (max number of physical pages per-zspage)
> by looking at a `used percentage` value. This is not enough
> as we lose precision during usage percentage calculations
> For example, let's look at size class 208:
> 
> pages per zspage       wasted bytes         used%
>        1                   144               96
>        2                    80               99
>        3                    16               99
>        4                   160               99
> 
> Current algorithm will select 2 page per zspage configuration,
> as it's the first one to reach 99%. However, 3 pages per zspage
> waste less memory.
> 
> Change algorithm and select zspage configuration that has
> lowest wasted value.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
Acked-by: Minchan Kim <minchan@...nel.org>