Re: [PATCH 3/9] migrate: add hugepage migration code to migrate_pages()

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Tue, Sep 10, 2013 at 03:33:26PM +0100, Mel Gorman wrote:
> On Fri, Aug 09, 2013 at 01:21:36AM -0400, Naoya Horiguchi wrote:
> > This patch extends check_range() to handle vma with VM_HUGETLB set.
> > We will be able to migrate hugepage with migrate_pages(2) after
> > applying the enablement patch which comes later in this series.
> > 
> > Note that for larger hugepages (covered by pud entries, 1GB for
> > x86_64 for example), we simply skip it now.
> > 
> > Note that using pmd_huge/pud_huge assumes that hugepages are pointed to
> > by pmd/pud. This is not true in some architectures implementing hugepage
> > with other mechanisms like ia64, but it's OK because pmd_huge/pud_huge
> > simply return 0 in such arch and page walker simply ignores such hugepages.
> > 
> > ChangeLog v4:
> >  - refactored check_hugetlb_pmd_range for better readability
> > 
> > ChangeLog v3:
> >  - revert introducing migrate_movable_pages
> >  - use isolate_huge_page
> > 
> > ChangeLog v2:
> >  - remove unnecessary extern
> >  - fix page table lock in check_hugetlb_pmd_range
> >  - updated description and renamed patch title
> > 
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > Acked-by: Andi Kleen <ak@linux.intel.com>
> > Reviewed-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
> > Acked-by: Hillf Danton <dhillf@gmail.com>
> > ---
> >  mm/mempolicy.c | 42 +++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 37 insertions(+), 5 deletions(-)
> > 
> > diff --git v3.11-rc3.orig/mm/mempolicy.c v3.11-rc3/mm/mempolicy.c
> > index 7431001..d96afc1 100644
> > --- v3.11-rc3.orig/mm/mempolicy.c
> > +++ v3.11-rc3/mm/mempolicy.c
> > @@ -512,6 +512,30 @@ static int check_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> >  	return addr != end;
> >  }
> >  
> > +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
> > +}
> > +
> >  static inline int check_pmd_range(struct vm_area_struct *vma, pud_t *pud,
> >  		unsigned long addr, unsigned long end,
> >  		const nodemask_t *nodes, unsigned long flags,
> > @@ -523,6 +547,11 @@ static inline int check_pmd_range(struct vm_area_struct *vma, pud_t *pud,
> >  	pmd = pmd_offset(pud, addr);
> >  	do {
> >  		next = pmd_addr_end(addr, end);
> > +		if (pmd_huge(*pmd) && is_vm_hugetlb_page(vma)) {
> > +			check_hugetlb_pmd_range(vma, pmd, nodes,
> > +						flags, private);
> > +			continue;
> > +		}
> >  		split_huge_page_pmd(vma, addr, pmd);
> >  		if (pmd_none_or_trans_huge_or_clear_bad(pmd))
> >  			continue;
> 
> If a hugepage is currently being migrated then a migration entry should
> be in its place which is a type of swap entry. Will the pmd_huge check
> still do the right thing if migration is already in progress?

Ah, we need migration entry check before pmd_huge check. Thank you.

Thanks,
Naoya Horiguchi

> 
> >  		if (check_pmd_range(vma, pud, addr, next, nodes,
> > @@ -635,9 +666,6 @@ check_range(struct mm_struct *mm, unsigned long start, unsigned long end,
> >  				return ERR_PTR(-EFAULT);
> >  		}
> >  
> > -		if (is_vm_hugetlb_page(vma))
> > -			goto next;
> > -
> >  		if (flags & MPOL_MF_LAZY) {
> >  			change_prot_numa(vma, start, endvma);
> >  			goto next;
> > @@ -986,7 +1014,11 @@ static void migrate_page_add(struct page *page, struct list_head *pagelist,
> >  
> >  static struct page *new_node_page(struct page *page, unsigned long node, int **x)
> >  {
> > -	return alloc_pages_exact_node(node, GFP_HIGHUSER_MOVABLE, 0);
> > +	if (PageHuge(page))
> > +		return alloc_huge_page_node(page_hstate(compound_head(page)),
> > +					node);
> > +	else
> > +		return alloc_pages_exact_node(node, GFP_HIGHUSER_MOVABLE, 0);
> >  }
> >  
> >  /*
> > @@ -1016,7 +1048,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
> >  		err = migrate_pages(&pagelist, new_node_page, dest,
> >  					MIGRATE_SYNC, MR_SYSCALL);
> >  		if (err)
> > -			putback_lru_pages(&pagelist);
> > +			putback_movable_pages(&pagelist);
> >  	}
> >  
> >  	return err;
> > -- 
> > 1.8.3.1
> > 
> 
> -- 
> Mel Gorman
> SUSE Labs
>

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