Re: [PATCH 5/9] migrate: enable migrate_pages() to migrate hugepage

[Simon Jeons <simon.jeons@gmail.com>]

Hi Naoya,
On 03/19/2013 08:07 AM, Naoya Horiguchi wrote:
> On Mon, Mar 18, 2013 at 04:40:57PM +0100, Michal Hocko wrote:
>> On Thu 21-02-13 14:41:44, Naoya Horiguchi wrote:
>>> This patch extends check_range() to handle vma with VM_HUGETLB set.
>>> With this changes, we can migrate hugepage with migrate_pages(2).
>>> Note that for larger hugepages (covered by pud entries, 1GB for
>>> x86_64 for example), we simply skip it now.
>>>
>>> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>>> ---
>>>  include/linux/hugetlb.h |  6 ++++--
>>>  mm/hugetlb.c            | 10 ++++++++++
>>>  mm/mempolicy.c          | 46 ++++++++++++++++++++++++++++++++++------------
>>>  3 files changed, 48 insertions(+), 14 deletions(-)
>>>
>>> diff --git v3.8.orig/include/linux/hugetlb.h v3.8/include/linux/hugetlb.h
>>> index 8f87115..eb33df5 100644
>>> --- v3.8.orig/include/linux/hugetlb.h
>>> +++ v3.8/include/linux/hugetlb.h
>>> @@ -69,6 +69,7 @@ void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed);
>>>  int dequeue_hwpoisoned_huge_page(struct page *page);
>>>  void putback_active_hugepage(struct page *page);
>>>  void putback_active_hugepages(struct list_head *l);
>>> +void migrate_hugepage_add(struct page *page, struct list_head *list);
>>>  void copy_huge_page(struct page *dst, struct page *src);
>>>  
>>>  extern unsigned long hugepages_treat_as_movable;
>>> @@ -88,8 +89,8 @@ struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
>>>  				pmd_t *pmd, int write);
>>>  struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
>>>  				pud_t *pud, int write);
>>> -int pmd_huge(pmd_t pmd);
>>> -int pud_huge(pud_t pmd);
>>> +extern int pmd_huge(pmd_t pmd);
>>> +extern int pud_huge(pud_t pmd);
>> extern is not needed here.
> OK.
>
>>>  unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
>>>  		unsigned long address, unsigned long end, pgprot_t newprot);
>>>  
>>> @@ -134,6 +135,7 @@ static inline int dequeue_hwpoisoned_huge_page(struct page *page)
>>>  
>>>  #define putback_active_hugepage(p) 0
>>>  #define putback_active_hugepages(l) 0
>>> +#define migrate_hugepage_add(p, l) 0
>>>  static inline void copy_huge_page(struct page *dst, struct page *src)
>>>  {
>>>  }
>>> diff --git v3.8.orig/mm/hugetlb.c v3.8/mm/hugetlb.c
>>> index cb9d43b8..86ffcb7 100644
>>> --- v3.8.orig/mm/hugetlb.c
>>> +++ v3.8/mm/hugetlb.c
>>> @@ -3202,3 +3202,13 @@ void putback_active_hugepages(struct list_head *l)
>>>  	list_for_each_entry_safe(page, page2, l, lru)
>>>  		putback_active_hugepage(page);
>>>  }
>>> +
>>> +void migrate_hugepage_add(struct page *page, struct list_head *list)
>>> +{
>>> +	VM_BUG_ON(!PageHuge(page));
>>> +	get_page(page);
>>> +	spin_lock(&hugetlb_lock);
>> Why hugetlb_lock? Comment for this lock says that it protects
>> hugepage_freelists, nr_huge_pages, and free_huge_pages.
> I think that this comment is out of date and hugepage_activelists,
> which was introduced recently, should be protected because this
> patchset adds is_hugepage_movable() which runs through the list.
> So I'll update the comment in the next post.
>
>>> +	list_move_tail(&page->lru, list);
>>> +	spin_unlock(&hugetlb_lock);
>>> +	return;
>>> +}
>>> diff --git v3.8.orig/mm/mempolicy.c v3.8/mm/mempolicy.c
>>> index e2df1c1..8627135 100644
>>> --- v3.8.orig/mm/mempolicy.c
>>> +++ v3.8/mm/mempolicy.c
>>> @@ -525,6 +525,27 @@ 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));
>>> +	spin_unlock(&vma->vm_mm->page_table_lock);
>> I am a bit confused why page_table_lock is used here and why it doesn't
>> cover the page usage.
> I expected this function to do the same for pmd as check_pte_range() does
> for pte, but the above code didn't do it. I should've put spin_unlock
> below migrate_hugepage_add(). Sorry for the confusion.

I still confuse! Could you explain more in details?

>
>>> +	nid = page_to_nid(page);
>>> +	if (node_isset(nid, *nodes) != !!(flags & MPOL_MF_INVERT)
>>> +	    && ((flags & MPOL_MF_MOVE && page_mapcount(page) == 1)
>>> +		|| flags & MPOL_MF_MOVE_ALL))
>>> +		migrate_hugepage_add(page, private);
>>> +#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,
>>> @@ -536,6 +557,11 @@ 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)) {
>> Why an explicit check for is_vm_hugetlb_page here? Isn't pmd_huge()
>> sufficient?
> I think we need both check here because if we use only pmd_huge(),
> pmd for thp goes into this branch wrongly. 
>
> Thanks,
> Naoya
>
>>> +			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;
>> [...]
>> -- 
>> Michal Hocko
>> SUSE Labs
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