Re: [RFC PATCH 1/3] mm, numa: rework do_pages_move

From: Michal Hocko <mhocko@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: linux-mm@kvack.org, Zi Yan <zi.yan@cs.rutgers.edu>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrea Reale <ar@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 1/3] mm, numa: rework do_pages_move
Date: Fri, 15 Dec 2017 10:28:59 +0100	[thread overview]
Message-ID: <20171215092859.GT16951@dhcp22.suse.cz> (raw)
In-Reply-To: <20171214153558.trgov6dbclav6ui7@node.shutemov.name>

On Thu 14-12-17 18:35:58, Kirill A. Shutemov wrote:
> On Wed, Dec 13, 2017 at 03:39:48PM +0100, Michal Hocko wrote:
[...]
> > +	err = 0;
> > +	if (page_to_nid(page) == node)
> > +		goto out_putpage;
> > +
> > +	err = -EACCES;
> > +	if (page_mapcount(page) > 1 &&
> > +			!migrate_all)
> 
> Non-sensible line break.

fixed

> > +		goto out_putpage;
> > +
> > +	if (PageHuge(page)) {
> > +		if (PageHead(page)) {
> > +			isolate_huge_page(page, pagelist);
> > +			err = 0;
> > +		}
> > +	} else {
> 
> Hm. I think if the page is PageTail() we have to split the huge page.
> If an user asks to migrate part of THP, we shouldn't migrate the whole page,
> otherwise it's not transparent anymore.

Well, as I've said in the cover letter. There are more things which are
worth considering but I've tried to keep the original semantic so
further changes should be done in separete patches. I will work on those
but I would prefer this to stay smaller if you do not mind.

> Otherwise, the patch looks good to me.

Thanks for the review
-- 
Michal Hocko
SUSE Labs