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

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Date:	Mon, 2 Feb 2015 16:06:29 +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 15:18), Minchan Kim wrote:
> > 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.
> 
> Sorry, I don't get it. Could you describe what you are concerning about active I/O?
> My concern is just race bd_holder/bd_openers and bd_holders of zram check.
> I don't think any simple solution without bd_mutex.
> If we can close the race, anything could be a solution.
> If we close the race, we should return -EBUSY if anyone is opening the zram device
> so bd_openers check would be better than bd_holders.
> 

yeah, sorry. nevermind.


So, guys, how about doing it differently, in less lines of code,
hopefully. Don't move reset_store()'s work to zram_reset_device().
Instead, move

	set_capacity(zram->disk, 0);
	revalidate_disk(zram->disk);

out from zram_reset_device() to reset_store(). this two function are
executed only when called from reset_store() anyway. this also will let
us drop `bool reset capacity' param from zram_reset_device().


so we will do in reset_store()

	mutex_lock(bdev->bd_mutex);

	fsync_bdev(bdev);
	zram_reset_device(zram);
	set_capacity(zram->disk, 0);

	mutex_unlock(&bdev->bd_mutex);

	revalidate_disk(zram->disk);
	bdput(bdev);



and change zram_reset_device(zram, false) call to simply zram_reset_device(zram)
in __exit zram_exit(void).

	-ss
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