linux-kernel - Re: [PATCH] zswap: only save zswap header if zpool is shrinkable

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Date:   Tue, 9 Jan 2018 13:48:17 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Dan Streetman <ddstreet@...e.org>,
        Seth Jennings <sjenning@...hat.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Nitin Gupta <ngupta@...are.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] zswap: only save zswap header if zpool is shrinkable

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