linux-kernel - Re: [PATCH 3/9] migrate: add hugepage migration code to migrate

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Message-Id: <20130814164100.e4ba87e694e3c6563c91bf0e@linux-foundation.org>
Date:	Wed, 14 Aug 2013 16:41:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	linux-mm@...ck.org, Mel Gorman <mgorman@...e.de>,
	Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	Hillf Danton <dhillf@...il.com>, Michal Hocko <mhocko@...e.cz>,
	Rik van Riel <riel@...hat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH 3/9] migrate: add hugepage migration code to
 migrate_pages()

On Fri,  9 Aug 2013 01:21:36 -0400 Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> +static void check_hugetlb_pmd_range(struct vm_area_struct *vma, pmd_t *pmd,
> +		const nodemask_t *nodes, unsigned long flags,
> +				    void *private)
> +{
> +#ifdef CONFIG_HUGETLB_PAGE
> +	int nid;
> +	struct page *page;
> +
> +	spin_lock(&vma->vm_mm->page_table_lock);
> +	page = pte_page(huge_ptep_get((pte_t *)pmd));
> +	nid = page_to_nid(page);
> +	if (node_isset(nid, *nodes) == !!(flags & MPOL_MF_INVERT))
> +		goto unlock;
> +	/* With MPOL_MF_MOVE, we migrate only unshared hugepage. */
> +	if (flags & (MPOL_MF_MOVE_ALL) ||
> +	    (flags & MPOL_MF_MOVE && page_mapcount(page) == 1))
> +		isolate_huge_page(page, private);
> +unlock:
> +	spin_unlock(&vma->vm_mm->page_table_lock);
> +#else
> +	BUG();
> +#endif
> +}

The function is poorly named.  What does it "check"?  And it does more
than checking things - at actually makes alterations!

Can we have a better name here please, and some docmentation explaining
what it does and why it does it?

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