linux-kernel - Re: [PATCH] mm: slub: fix page->

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Message-ID: <20140129064350.GA20252@localhost>
Date:	Wed, 29 Jan 2014 14:43:50 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Dave Hansen <dave@...1.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	penberg@...nel.org, mpm@...enic.com, pshelar@...ira.com
Subject: Re: [PATCH] mm: slub: fix page->_count corruption (again)

On Tue, Jan 28, 2014 at 03:52:47PM -0800, Dave Hansen wrote:
> On 01/28/2014 03:29 PM, Andrew Morton wrote:
> > On Tue, 28 Jan 2014 15:17:22 -0800 Dave Hansen <dave@...1.net> wrote:
> > This code is borderline insane.
> 
> No argument here.
> 
> > Yes, struct page is special and it's worth spending time and doing
> > weird things to optimise it.  But sheesh.
> > 
> > An alternative is to make that cmpxchg quietly go away.  Is it more
> > trouble than it is worth?
> 
> It has measurable performance benefits, and the benefits go up as the
> cost of en/disabling interrupts goes up (like if it takes you a hypercall).
> 
> Fengguang, could you run a set of tests for the top patch in this branch
> to see if we'd be giving much up by axing the code?
> 
> 	https://github.com/hansendc/linux/tree/slub-nocmpxchg-for-Fengguang-20140128

Sure, I've queued tests for the branch. Will report back after 1-2
days.

Thanks,
Fengguang

> I was talking with one of the distros about turning it off as well.
> They mentioned that they saw a few performance regressions when it was
> turned off.  I'll share details when I get them.
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