linux-kernel - RE: Subject: [PATCH V7 2/4] mm: frontswap: core code

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Message-ID: <4be6abb6-7b82-4e64-9e27-cd0fe0c1e1b1@default>
Date:	Mon, 29 Aug 2011 08:47:59 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
	hughd@...gle.com, ngupta@...are.org,
	Konrad Wilk <konrad.wilk@...cle.com>, JBeulich@...ell.com,
	Kurt Hackel <kurt.hackel@...cle.com>, npiggin@...nel.dk,
	akpm@...ux-foundation.org, riel@...hat.com, hannes@...xchg.org,
	matthew@....cx, Chris Mason <chris.mason@...cle.com>,
	sjenning@...ux.vnet.ibm.com, jackdachef@...il.com,
	cyclonusj@...il.com
Subject: RE: Subject: [PATCH V7 2/4] mm: frontswap: core code

> > My concern was race in counters. Even you allow race in frontswap_succ_puts++,
> >
> > Don't you need some lock for
> > 	sis->frontswap_pages++
> > 	sis->frontswap_pages--
> 
> Hmmm... OK, you've convinced me.  If this counter should be one and
> a race leaves it as zero, I think data corruption could result on
> a swapoff or partial swapoff.  And after thinking about it, I
> think I also need to check for locking on frontswap_set/clear
> as I don't think these bitfield modifiers are atomic.
> 
> Thanks for pointing this out.  Good catch!  I will need to
> play with this and test it so probably will not submit V8 until
> next week as today is a vacation day for me.

Silly me: Of course set_bit and clear_bit ARE atomic.  I will
post V8 later today with the only changes being frontswap_pages
is now a type atomic_t.

Thanks again for catching this, Kame!

Thanks,
Dan
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