linux-kernel - Re: [RFC 08/12] lockdep: Apply crossrelease to PG

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Date:	Mon, 4 Jul 2016 13:30:57 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, walken@...gle.com
Subject: Re: [RFC 08/12] lockdep: Apply crossrelease to PG_locked lock

On Fri, Jul 01, 2016 at 02:18:46PM +0300, Kirill A. Shutemov wrote:
> On Fri, Jul 01, 2016 at 08:21:21AM +0900, Byungchul Park wrote:
> > On Thu, Jun 30, 2016 at 03:04:58PM +0200, Peter Zijlstra wrote:
> > > On Mon, Jun 20, 2016 at 01:55:23PM +0900, Byungchul Park wrote:
> > > > @@ -215,6 +219,11 @@ struct page {
> > > >  #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
> > > >  	int _last_cpupid;
> > > >  #endif
> > > > +
> > > > +#ifdef CONFIG_LOCKDEP_PAGELOCK
> > > > +	struct lockdep_map map;
> > > > +	struct cross_lock xlock;
> > > > +#endif
> > > >  }
> > > 
> > > So that's 32+64=96 bytes (CONFIG_LOCK_STAT=n) added to struct page,
> > > really!?
> > 
> > Yes... I concerned it at first, but I thought it would be ok since
> > CONFIG_LOCKDEP_PAGE is a debug feature. Anyway, I will try to reduce
> > the size of struct cross_lock which is only thing I can do to reduce
> > it, since we cannot avoid using lockdep_map if we want to make
> > lock_page() participate in the lockdep play.
> 
> Please use page_ext instead. With boottime switch to enable.
> 
> This way we can have this compile-time debug option enabled on more
> machines without unnecessary runtime overhead.

Thank you for advice.

I also think it's one of good candidates except the fact that it have to
depend on page_ext additionally.

> 
> And, please, CC linux-mm next time.
> 
> -- 
>  Kirill A. Shutemov