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Date:   Mon, 17 Oct 2022 17:08:50 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv3 4/8] zram: Introduce recompress sysfs knob
Message-Id: <20221017170850.034705ad83c54b92236d14f7@linux-foundation.org>
In-Reply-To: <20221009090720.1040633-5-senozhatsky@chromium.org>
References: <20221009090720.1040633-1-senozhatsky@chromium.org>
        <20221009090720.1040633-5-senozhatsky@chromium.org>
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On Sun,  9 Oct 2022 18:07:16 +0900 Sergey Senozhatsky <senozhatsky@chromium.org> wrote:

> Allow zram to recompress (using secondary compression streams)
> pages. We support three modes:
> 
> 1) IDLE pages recompression is activated by `idle` mode
> 
> 	echo idle > /sys/block/zram0/recompress
> 
> 2) Since there may be many idle pages user-space may pass a size
> watermark value and we will recompress IDLE pages only of equal
> or greater size:
> 
> 	echo 888 > /sys/block/zram0/recompress

It's helpful to describe the units ("bytes") here and in the
docmentation.

> 3) HUGE pages recompression is activated by `huge` mode
> 
> 	echo huge > /sys/block/zram0/recompress
> 
> 4) HUGE_IDLE pages recompression is activated by `huge_idle` mode
> 
> 	echo huge_idle > /sys/block/zram0/recompress
> 
> ...
>
> +	if (IS_ERR((void *)handle_next)) {

IS_ERR_VALUE() avoids castsing back and forth.