linux-kernel - Re: [PATCH v2 1/2] mm: free compound page with correct order

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Message-ID: <20141015200501.GA17066@node.dhcp.inet.fi>
Date:	Wed, 15 Oct 2014 23:05:01 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Yu Zhao <yuzhao@...gle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Hugh Dickins <hughd@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Bob Liu <lliubbo@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	David Rientjes <rientjes@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: free compound page with correct order

On Wed, Oct 15, 2014 at 12:30:44PM -0700, Andrew Morton wrote:
> > @@ -232,7 +232,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
> >  	if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
> >  		struct page *zero_page = xchg(&huge_zero_page, NULL);
> >  		BUG_ON(zero_page == NULL);
> > -		__free_page(zero_page);
> > +		__free_pages(zero_page, compound_order(zero_page));
> 
> But I'm surprised that this is also rare.  It makes me wonder if this
> code is working correctly.

This should be rare too. To get here we need a situation when huge zero
page is allocated, but not mapped and we get memory presure to trigger
shrinker.

-- 
 Kirill A. Shutemov
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