linux-kernel - Re: [PATCH 15/22] Do not disable interrupts in free_page

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Message-Id: <20090424090552.1044.A69D9226@jp.fujitsu.com>
Date:	Fri, 24 Apr 2009 09:07:13 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Mel Gorman <mel@....ul.ie>,
	linux-mm@...ck.org, cl@...ux-foundation.org, npiggin@...e.de,
	linux-kernel@...r.kernel.org, ming.m.lin@...el.com,
	yanmin_zhang@...ux.intel.com, peterz@...radead.org,
	penberg@...helsinki.fi
Subject: Re: [PATCH 15/22] Do not disable interrupts in free_page_mlock()

> > @@ -556,6 +555,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> >  	unsigned long flags;
> >  	int i;
> >  	int bad = 0;
> > +	int clearMlocked = PageMlocked(page);
> >  
> >  	for (i = 0 ; i < (1 << order) ; ++i)
> >  		bad += free_pages_check(page + i);
> > @@ -571,6 +571,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> >  	kernel_map_pages(page, 1 << order, 0);
> >  
> >  	local_irq_save(flags);
> > +	if (unlikely(clearMlocked))
> > +		free_page_mlock(page);
> 
> I wonder what the compiler does in the case
> CONFIG_HAVE_MLOCKED_PAGE_BIT=n.  If it is dumb, this patch would cause
> additional code generation.

if CONFIG_HAVE_MLOCKED_PAGE_BIT=n, PageMlocked() is {return 0;} then
gcc can remove following code, I think.
	if (0) 
		free_page_mlock(page)



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