linux-kernel - Re: [PATCH 5/10] mm/memcg: introduce page_relock

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Message-ID: <alpine.LSU.2.00.1202211426010.2012@eggly.anvils>
Date:	Tue, 21 Feb 2012 14:36:56 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Ying Han <yinghan@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/10] mm/memcg: introduce page_relock_lruvec

On Tue, 21 Feb 2012, KAMEZAWA Hiroyuki wrote:
> 
> No perforamce impact by replacing spin_lock_irq()/spin_unlock_irq() to
> spin_lock_irqsave() and spin_unlock_irqrestore() ?

None that I noticed - but that is not at all a reassuring answer!

It worries me a little.  I think it would make more or less difference
on different architectures, and I forget where x86 stands there - one
of the more or the less affected?  Worth branches down inside
page_relock_lruvec()?

It's also unfortunate to be "losing" the information of where _irq
is needed and where _irqsave (but not much gets lost with git).

It's something that can be fixed - and I think Konstantin's version
already keeps the variants: I just didn't want to get confused by them,
while focussing on the locking details.

Hugh
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