Subject: Re: [RFC PATCH 1/3] mm, numa: rework do_pages_move
To: Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org
References: <20171207143401.GK20234@dhcp22.suse.cz>
 <20171208161559.27313-1-mhocko@kernel.org>
 <20171208161559.27313-2-mhocko@kernel.org>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Reale <ar@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@suse.com>
From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Date: Tue, 2 Jan 2018 16:55:46 +0530
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On 12/08/2017 09:45 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> do_pages_move is supposed to move user defined memory (an array of
> addresses) to the user defined numa nodes (an array of nodes one for
> each address). The user provided status array then contains resulting
> numa node for each address or an error. The semantic of this function is
> little bit confusing because only some errors are reported back. Notably
> migrate_pages error is only reported via the return value. This patch

It does report back the migration failures as well. In new_page_node
there is '*result = &pm->status' which going forward in unmap_and_move
will hold migration error or node ID of the new page.

	newpage = get_new_page(page, private, &result);
	............
	if (result) {
		if (rc)
			*result = rc;
		else
			*result = page_to_nid(newpage);
	}