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Date: Mon, 18 Mar 2013 20:07:16 -0400
From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To: Michal Hocko <mhocko@...e.cz>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] migrate: enable migrate_pages() to migrate hugepage
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@...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.
> > + 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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