linux-kernel - Re: [PATCH] staging: zcache: fix serialization bug in zv stats

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Message-ID: <20120103213812.GL17472@phenom.dumpdata.com>
Date:	Tue, 3 Jan 2012 16:38:12 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Brian King <brking@...ux.vnet.ibm.com>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
	Nitin Gupta <ngupta@...are.org>
Subject: Re: [PATCH] staging: zcache: fix serialization bug in zv stats

On Fri, Dec 30, 2011 at 11:35:45AM -0600, Seth Jennings wrote:
> On 12/30/2011 11:02 AM, Dan Magenheimer wrote:
> >> From: Seth Jennings [mailto:sjenning@...ux.vnet.ibm.com]
> >> Sent: Friday, December 30, 2011 9:42 AM
> >> To: Greg Kroah-Hartman
> >> Cc: Seth Jennings; Dan Magenheimer; Brian King; devel@...verdev.osuosl.org; linux-
> >> kernel@...r.kernel.org
> >> Subject: [PATCH] staging: zcache: fix serialization bug in zv stats
> >>
> >> In a multithreaded workload, the zv_curr_dist_counts
> >> and zv_cumul_dist_counts statistics are being corrupted
> >> because the increments and decrements in zv_create
> >> and zv_free are not atomic.
> >>
> >> This patch converts these statistics and their corresponding
> >> increments/decrements/reads to atomic operations.
> >>
> >> Based on v3.2-rc7
> >>
> >> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> > 
> > I'm inclined to nack this change, at least unless inside an #ifdef DEBUG,
> 
> I guess I didn't respond to this suggestion.  We could put #ifdef DEBUG
> around the updates in zv_create and zv_free and around the two sysfs
> *_show functions.  Kinda messy though.  I guess it might not matter
> if we'll be re-evaluating this whole thing soon.

Perhaps also add in the TODO file that we want to move the stats collection
out of the code and only be enabled if CONFIG_DEBUGFS is set? (Which granted means
we need to implement the stats output in debugfs instead of sysfs).
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