linux-kernel - Re: [PATCH v1 2/2] zram: remove init_lock in zram_make

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Date:	Mon, 2 Feb 2015 14:59:23 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, Nitin Gupta <ngupta@...are.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Ganesh Mahendran <opensource.ganesh@...il.com>
Subject: Re: [PATCH v1 2/2] zram: remove init_lock in zram_make_request

On (02/02/15 12:41), Minchan Kim wrote:
> > If we use zram as block device itself(not a fs or swap) and open the
> > block device as !FMODE_EXCL, bd_holders will be void.
> > 
> > Another topic: As I didn't see enough fs/block_dev.c bd_holders in zram
> > would be mess. I guess we need to study hotplug of device and implement
> > it for zram reset rather than strange own konb. It should go TODO. :(
> 
> Actually, I thought bd_mutex use from custom driver was terrible idea
> so we should walk around with device hotplug but as I look through
> another drivers, they have used the lock for a long time.
> Maybe it's okay to use it in zram?
> If so, Ganesh's patch is no problem to me although I didn't' review it in detail.
> One thing I want to point out is that it would be better to change bd_holders
> with bd_openers to filter out because dd test opens block device as !EXCL
> so bd_holders will be void.
> 
> What do you think about it?
> 

a quick idea:
can we additionally move all bd flush and put work after zram_reset_device(zram, true)
and, perhaps, replace ->bd_holders with something else?

zram_reset_device() will not return until we have active IOs, pending IOs will be
invalidated by ->disksize != 0.

	-ss
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