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Date: Thu, 11 Jan 2018 15:57:57 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH] zswap: only save zswap header if zpool is shrinkable
Message-ID: <20180111065757.GG494@jagdpanzerIV>
References: <20180108225101.15790-1-yuzhao@google.com>
 <CALZtONCsC79jyCsFQcJOALhw=QrTeFMiYTpE+HRrVjMh-QeT-g@mail.gmail.com>
 <20180109224700.GA175231@google.com>
 <CALZtONDc3VkWg83y1Nv_q+yUmwuFWmPUrFQOTJQv6b_ZbOh49g@mail.gmail.com>
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To: Dan Streetman <ddstreet@ieee.org>
Cc: Yu Zhao <yuzhao@google.com>, 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 <linux-mm@kvack.org>, linux-kernel <linux-kernel@vger.kernel.org>

Hello,

Yu Zhao, Dan, sorry for the delay


On (01/10/18 15:06), Dan Streetman wrote:
[..]
> Well, I think shrink vs evict an implementation detail, isn't it?
> That is, from zswap's perspective, there should be:
> 
> zpool_evictable()
> if true, zswap needs to include the header on each compressed page,
> because the zpool may callback zpool->ops->evict() which calls
> zswap_writeback_entry() which expects the entry to start with a zswap
> header.
> if false, zswap doesn't need to include the header, because the zpool
> will never, ever call zpool->ops->evict
> 
> zpool_shrink()
> this will try to shrink the zpool, using whatever
> zpool-implementation-specific shrinking method.  If zpool_evictable()
> is true for this zpool, then zpool_shrink() *might* callback to
> zpool->ops->evict(), although it doesn't have to if it can shrink
> without evictions.  If zpool_evictable() is false, then zpool_shrink()
> will never callback to zpool->ops->evict().

ACK on this!

	-ss

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