Re: [PATCH 01/19] mm, thp: drop FOLL_SPLIT

From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>,
	Rik van Riel <riel@redhat.com>, Vlastimil Babka <vbabka@suse.cz>,
	Christoph Lameter <cl@gentwo.org>,
	Steve Capper <steve.capper@linaro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@suse.cz>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH 01/19] mm, thp: drop FOLL_SPLIT
Date: Tue, 25 Nov 2014 16:04:28 +0200	[thread overview]
Message-ID: <20141125140428.GA11841@node.dhcp.inet.fi> (raw)
In-Reply-To: <20141125030109.GA21716@hori1.linux.bs1.fc.nec.co.jp>

On Tue, Nov 25, 2014 at 03:01:16AM +0000, Naoya Horiguchi wrote:
> On Wed, Nov 05, 2014 at 04:49:36PM +0200, Kirill A. Shutemov wrote:
> > FOLL_SPLIT is used only in two places: migration and s390.
> > 
> > Let's replace it with explicit split and remove FOLL_SPLIT.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> ...
> > @@ -1246,6 +1246,11 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
> >  		if (!page)
> >  			goto set_status;
> >  
> > +		if (PageTransHuge(page) && split_huge_page(page)) {
> > +			err = -EBUSY;
> > +			goto set_status;
> > +		}
> > +
> 
> This check makes split_huge_page() be called for hugetlb pages, which
> triggers BUG_ON. So could you do this after if (PageHuge) block below?
> And I think that we have "Node already in the right place" check afterward,
> so I hope that moving down this check also helps us reduce thp splitting.

It makes sense. Thanks for report.

Other problem here is that we need to goto put_and_set, not set_status :-/

-- 
 Kirill A. Shutemov