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Date: Sun, 21 May 2017 00:04:27 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Minchan Kim <minchan@kernel.org>
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Subject: Re: [PATCH 2/2] zram: do not count duplicated pages as compressed
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 <20170517083212.GA25750@bbox>
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On Wed, May 17, 2017 at 05:32:12PM +0900, Minchan Kim wrote:
> Is block device(esp, zram which is compressed ram block device) okay to
> return garbage when ongoing overwrite IO fails?
> 
> O_DIRECT write 4 block "aaa.." -> success
> read  4 block "aaa.." -> success
> O_DIRECT write 4 block "bbb.." -> fail
> read  4 block "000..' -> it is okay?
> 
> Hope to get an answer form experts. :)

It's "okay" as it's what existing real block devices do (at least on a
sector boundary).  It's not "nice" though, so if you can avoid it,
please do.