linux-kernel - Re: [PATCH 22/49] mm: mempolicy: Add MPOL_MF

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Message-ID: <20130107151430.GL3885@suse.de>
Date:	Mon, 7 Jan 2013 15:14:30 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Hillf Danton <dhillf@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Alex Shi <lkml.alex@...il.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 22/49] mm: mempolicy: Add MPOL_MF_LAZY

On Fri, Jan 04, 2013 at 11:18:17PM -0600, Simon Jeons wrote:
> > +static int
> > +change_prot_numa_range(struct mm_struct *mm, struct vm_area_struct *vma,
> > +			unsigned long address)
> > +{
> > +	pgd_t *pgd;
> > +	pud_t *pud;
> > +	pmd_t *pmd;
> > +	pte_t *pte, *_pte;
> > +	struct page *page;
> > +	unsigned long _address, end;
> > +	spinlock_t *ptl;
> > +	int ret = 0;
> > +
> > +	VM_BUG_ON(address & ~PAGE_MASK);
> > +
> > +	pgd = pgd_offset(mm, address);
> > +	if (!pgd_present(*pgd))
> > +		goto out;
> > +
> > +	pud = pud_offset(pgd, address);
> > +	if (!pud_present(*pud))
> > +		goto out;
> > +
> > +	pmd = pmd_offset(pud, address);
> > +	if (pmd_none(*pmd))
> > +		goto out;
> > +
> > +	if (pmd_trans_huge_lock(pmd, vma) == 1) {
> > +		int page_nid;
> > +		ret = HPAGE_PMD_NR;
> > +
> > +		VM_BUG_ON(address & ~HPAGE_PMD_MASK);
> > +
> > +		if (pmd_numa(*pmd)) {
> > +			spin_unlock(&mm->page_table_lock);
> > +			goto out;
> > +		}
> > +
> > +		page = pmd_page(*pmd);
> > +
> > +		/* only check non-shared pages */
> > +		if (page_mapcount(page) != 1) {
> > +			spin_unlock(&mm->page_table_lock);
> > +			goto out;
> > +		}
> > +
> > +		page_nid = page_to_nid(page);
> > +
> > +		if (pmd_numa(*pmd)) {
> > +			spin_unlock(&mm->page_table_lock);
> > +			goto out;
> > +		}
> > +
> 
> Hi Gorman,
> 
> Since pmd_trans_huge_lock has already held &mm->page_table_lock, then
> why check pmd_numa(*pmd) again?
> 

It looks like oversight. I've added a TODO item to clean it up when I
revisit NUMA balancing some time soon.

Thanks.

-- 
Mel Gorman
SUSE Labs
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