linux-kernel - Re: [PATCH 2/2] zram: do not count duplicated pages as compressed

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Message-ID: <20170521071536.GA9377@bgram>
Date:   Sun, 21 May 2017 16:15:36 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel-team <kernel-team@....com>, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, viro@...iv.linux.org.uk,
        axboe@...nel.dk, jlayton@...hat.com, tytso@....edu
Subject: Re: [PATCH 2/2] zram: do not count duplicated pages as compressed

On Sun, May 21, 2017 at 12:04:27AM -0700, Christoph Hellwig wrote:
> 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.

That was my understanding so I wanted to avoid it for just simple
code refactoring. Your comment helps to confirm the thhought.

Thanks, Christoph!