linux-kernel - Re: [PATCH 05/10] migrate: add hugepage migration code to migrate

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Date:	Tue, 26 Mar 2013 09:55:35 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
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>,
	Hillf Danton <dhillf@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/10] migrate: add hugepage migration code to
 migrate_pages()

On Tue 26-03-13 01:13:10, Naoya Horiguchi wrote:
> On Mon, Mar 25, 2013 at 02:04:16PM +0100, Michal Hocko wrote:
> > On Fri 22-03-13 16:23:50, Naoya Horiguchi wrote:
[...]
> > > @@ -1012,14 +1040,8 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
> > >  	check_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
> > >  			flags | MPOL_MF_DISCONTIG_OK, &pagelist);
> > >  
> > > -	if (!list_empty(&pagelist)) {
> > > -		err = migrate_pages(&pagelist, new_node_page, dest,
> > > +	return migrate_movable_pages(&pagelist, new_node_page, dest,
> > >  					MIGRATE_SYNC, MR_SYSCALL);
> > > -		if (err)
> > > -			putback_lru_pages(&pagelist);
> > > -	}
> > > -
> > > -	return err;
> > 
> > This is really confusing. Why migrate_pages doesn't do putback cleanup
> > on its own but migrate_movable_pages does?
> 
> I consider migrate_movable_pages() as a wrapper of migrate_pages(),
> not the variant of migrate_pages().

The naming suggests that this is the same functionality for a "different"
type of pages.

> We can find the same pattern in the callers like
> 
>   if (!list_empty(&pagelist)) {
>         err = migrate_pages(...);
>         if (err)
>                 putback_lru_pages(&pagelist);
>   }
> 
> , so it can be simplified by migrate_movable_pages().

I would rather see the same pattern for both. It could be error prone if

-- 
Michal Hocko
SUSE Labs
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