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

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Date:	Mon, 2 Feb 2015 13:01:24 +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 11:44), Minchan Kim wrote:
> > sure, I did think about this. and I actually didn't find any reason not
> > to use ->refcount there. if user wants to reset the device, he first
> > should umount it to make bdev->bd_holders check happy. and that's where
> > IOs will be failed. so it makes sense to switch to ->refcount there, IMHO.
> 
> 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.
> 

hm.
I don't mind to use ->disksize there, but personally I'd maybe prefer
to use ->refcount, which just looks less hacky. zram's most common use
cases are coming from ram swap device or ram device with fs. so it looks
a bit like we care about some corner case here.

just my opinion, no objections against ->disksize != 0.

I need to check fs/block_dev. can we switch away from ->bd_holders?

> 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. :(

ok, need to investigate this later.
let's land current activities first.

	-ss
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