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Date: Tue, 9 Jan 2018 13:48:17 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH] zswap: only save zswap header if zpool is shrinkable
Message-ID: <20180109044817.GB6953@jagdpanzerIV>
References: <20180108225101.15790-1-yuzhao@google.com>
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Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Yu Zhao <yuzhao@google.com>
Cc: Dan Streetman <ddstreet@ieee.org>, Seth Jennings <sjenning@redhat.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Minchan Kim <minchan@kernel.org>, Nitin Gupta <ngupta@vflare.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On (01/08/18 14:51), Yu Zhao wrote:
[..]
>  int zpool_shrink(struct zpool *zpool, unsigned int pages,
>  			unsigned int *reclaimed)
>  {
> -	return zpool->driver->shrink(zpool->pool, pages, reclaimed);
> +	return zpool_shrinkable(zpool) ?
> +	       zpool->driver->shrink(zpool->pool, pages, reclaimed) : -EINVAL;
>  }
>  
>  /**
> @@ -355,6 +356,20 @@ u64 zpool_get_total_size(struct zpool *zpool)
>  	return zpool->driver->total_size(zpool->pool);
>  }
>  
> +/**
> + * zpool_shrinkable() - Test if zpool is shrinkable
> + * @pool	The zpool to test
> + *
> + * Zpool is only shrinkable when it's created with struct
> + * zpool_ops.evict and its driver implements struct zpool_driver.shrink.
> + *
> + * Returns: true if shrinkable; false otherwise.
> + */
> +bool zpool_shrinkable(struct zpool *zpool)
> +{
> +	return zpool->ops && zpool->ops->evict && zpool->driver->shrink;
> +}

just a side note,
it might be a bit confusing and maybe there is a better
name for it. zsmalloc is shrinkable (we register a shrinker
callback), but not in the way zpool defines it.

	-ss

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