linux-kernel - Re: [rfc] optimise unlock

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Message-ID: <20070508223518.GC20174@wotan.suse.de>
Date:	Wed, 9 May 2007 00:35:18 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	David Howells <dhowells@...hat.com>
Cc:	linux-arch@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [rfc] optimise unlock_page

On Tue, May 08, 2007 at 01:13:35PM +0100, David Howells wrote:
> 
> Nick Piggin <npiggin@...e.de> wrote:
> 
> > This patch trades a page flag for a significant improvement in the unlock_page
> > fastpath. Various problems in the previous version were spotted by Hugh and
> > Ben (and fixed in this one).
> 
> It looks reasonable at first glance, though it does consume yet another page
> flag:-/  However, I think that's probably a worthy trade.

Well, that's the big question :)


> >  }
> > -	
> > +
> > +static inline void unlock_page(struct page *page)
> > +{
> > +	VM_BUG_ON(!PageLocked(page));
> > +	ClearPageLocked_Unlock(page);
> > +	if (unlikely(PageWaiters(page)))
> > +		__unlock_page(page);
> > +}
> > +
> 
> Please don't simply discard the documentation, we have little enough as it is:

Oops, right.

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