linux-kernel - Re: [PATCH 1/9] migrate: add migrate_entry_wait

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Date:	Mon, 18 Mar 2013 20:06:23 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/9] migrate: add migrate_entry_wait_huge()

On Mon, Mar 18, 2013 at 03:51:59PM +0100, Michal Hocko wrote:
> On Thu 21-02-13 14:41:40, Naoya Horiguchi wrote:
> [...]
> > diff --git v3.8.orig/mm/migrate.c v3.8/mm/migrate.c
> > index 2fd8b4a..7d84f4c 100644
> > --- v3.8.orig/mm/migrate.c
> > +++ v3.8/mm/migrate.c
> > @@ -236,6 +236,30 @@ void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> >  	pte_unmap_unlock(ptep, ptl);
> >  }
> >  
> > +void migration_entry_wait_huge(struct mm_struct *mm, pmd_t *pmd,
> > +				unsigned long address)
> > +{
> > +	spinlock_t *ptl = pte_lockptr(mm, pmd);
> > +	pte_t pte;
> > +	swp_entry_t entry;
> > +	struct page *page;
> > +
> > +	spin_lock(ptl);
> > +	pte = huge_ptep_get((pte_t *)pmd);
> > +	if (!is_hugetlb_entry_migration(pte))
> > +		goto out;
> > +	entry = pte_to_swp_entry(pte);
> > +	page = migration_entry_to_page(entry);
> > +	if (!get_page_unless_zero(page))
> > +		goto out;
> > +	spin_unlock(ptl);
> > +	wait_on_page_locked(page);
> > +	put_page(page);
> > +	return;
> > +out:
> > +	spin_unlock(ptl);
> > +}
> 
> This duplicates a lot of code from migration_entry_wait. Can we just
> teach the generic one to be HugePage aware instead?
> All it takes is just opencoding pte_offset_map_lock and calling
> huge_ptep_get ofr HugePage and pte_offset_map otherwise.

Yes, it's possible with some cleanup. I'll do this.

Thanks,
Naoya
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