Date: Tue, 9 Jan 2018 03:01:41 -0800
From: Yu Zhao <yuzhao@google.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Dan Streetman <ddstreet@ieee.org>,
        Seth Jennings <sjenning@redhat.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
Subject: Re: [PATCH] zswap: only save zswap header if zpool is shrinkable
Message-ID: <20180109110141.GA91365@google.com>
References: <20180108225101.15790-1-yuzhao@google.com>
 <20180109044817.GB6953@jagdpanzerIV>
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On Tue, Jan 09, 2018 at 01:48:17PM +0900, Sergey Senozhatsky wrote:
> 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.

Thanks. Do zpool_evictable() and zpool->driver->evict make more sense?