Re: [PATCH 20/23] thp: handle file pages in split_huge_page()

[Ning Qu <quning@google.com>]

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Is this safe to move the vma_adjust_trans_huge before the line 772? Seems
for anonymous memory, we only take the lock after vma_adjust_trans_huge,
maybe we should do the same for file?

Best wishes,
-- 
Ning Qu (曲宁) | Software Engineer | quning@google.com | +1-408-418-6066


On Tue, Aug 6, 2013 at 12:09 PM, Ning Qu <quning@google.com> wrote:

> I am probably running into a deadlock case for this patch.
>
> When splitting the file huge page, we hold the i_mmap_mutex.
>
> However, when coming from the call path in vma_adjust as following, we
> will grab the i_mmap_mutex already before doing vma_adjust_trans_huge,
> which will eventually calls the split_huge_page then split_file_huge_page
> ....
>
>
> https://git.kernel.org/cgit/linux/kernel/git/kas/linux.git/tree/mm/mmap.c?h=thp/pagecache#n753
>
>
>
>
> Best wishes,
> --
> Ning Qu (曲宁) | Software Engineer | quning@google.com | +1-408-418-6066
>
>
> On Sat, Aug 3, 2013 at 7:17 PM, Kirill A. Shutemov <
> kirill.shutemov@linux.intel.com> wrote:
>
>> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>>
>> The base scheme is the same as for anonymous pages, but we walk by
>> mapping->i_mmap rather then anon_vma->rb_root.
>>
>> When we add a huge page to page cache we take only reference to head
>> page, but on split we need to take addition reference to all tail pages
>> since they are still in page cache after splitting.
>>
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> ---
>>  mm/huge_memory.c | 89
>> +++++++++++++++++++++++++++++++++++++++++++++++---------
>>  1 file changed, 76 insertions(+), 13 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 523946c..d7c6830 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1580,6 +1580,7 @@ static void __split_huge_page_refcount(struct page
>> *page,
>>         struct zone *zone = page_zone(page);
>>         struct lruvec *lruvec;
>>         int tail_count = 0;
>> +       int initial_tail_refcount;
>>
>>         /* prevent PageLRU to go away from under us, and freeze lru stats
>> */
>>         spin_lock_irq(&zone->lru_lock);
>> @@ -1589,6 +1590,13 @@ static void __split_huge_page_refcount(struct page
>> *page,
>>         /* complete memcg works before add pages to LRU */
>>         mem_cgroup_split_huge_fixup(page);
>>
>> +       /*
>> +        * When we add a huge page to page cache we take only reference
>> to head
>> +        * page, but on split we need to take addition reference to all
>> tail
>> +        * pages since they are still in page cache after splitting.
>> +        */
>> +       initial_tail_refcount = PageAnon(page) ? 0 : 1;
>> +
>>         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
>>                 struct page *page_tail = page + i;
>>
>> @@ -1611,8 +1619,9 @@ static void __split_huge_page_refcount(struct page
>> *page,
>>                  * atomic_set() here would be safe on all archs (and
>>                  * not only on x86), it's safer to use atomic_add().
>>                  */
>> -               atomic_add(page_mapcount(page) + page_mapcount(page_tail)
>> + 1,
>> -                          &page_tail->_count);
>> +               atomic_add(initial_tail_refcount + page_mapcount(page) +
>> +                               page_mapcount(page_tail) + 1,
>> +                               &page_tail->_count);
>>
>>                 /* after clearing PageTail the gup refcount can be
>> released */
>>                 smp_mb();
>> @@ -1651,23 +1660,23 @@ static void __split_huge_page_refcount(struct
>> page *page,
>>                 */
>>                 page_tail->_mapcount = page->_mapcount;
>>
>> -               BUG_ON(page_tail->mapping);
>>                 page_tail->mapping = page->mapping;
>>
>>                 page_tail->index = page->index + i;
>>                 page_nid_xchg_last(page_tail, page_nid_last(page));
>>
>> -               BUG_ON(!PageAnon(page_tail));
>>                 BUG_ON(!PageUptodate(page_tail));
>>                 BUG_ON(!PageDirty(page_tail));
>> -               BUG_ON(!PageSwapBacked(page_tail));
>>
>>                 lru_add_page_tail(page, page_tail, lruvec, list);
>>         }
>>         atomic_sub(tail_count, &page->_count);
>>         BUG_ON(atomic_read(&page->_count) <= 0);
>>
>> -       __mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
>> +       if (PageAnon(page))
>> +               __mod_zone_page_state(zone,
>> NR_ANON_TRANSPARENT_HUGEPAGES, -1);
>> +       else
>> +               __mod_zone_page_state(zone,
>> NR_FILE_TRANSPARENT_HUGEPAGES, -1);
>>
>>         ClearPageCompound(page);
>>         compound_unlock(page);
>> @@ -1767,7 +1776,7 @@ static int __split_huge_page_map(struct page *page,
>>  }
>>
>>  /* must be called with anon_vma->root->rwsem held */
>> -static void __split_huge_page(struct page *page,
>> +static void __split_anon_huge_page(struct page *page,
>>                               struct anon_vma *anon_vma,
>>                               struct list_head *list)
>>  {
>> @@ -1791,7 +1800,7 @@ static void __split_huge_page(struct page *page,
>>          * and establishes a child pmd before
>>          * __split_huge_page_splitting() freezes the parent pmd (so if
>>          * we fail to prevent copy_huge_pmd() from running until the
>> -        * whole __split_huge_page() is complete), we will still see
>> +        * whole __split_anon_huge_page() is complete), we will still see
>>          * the newly established pmd of the child later during the
>>          * walk, to be able to set it as pmd_trans_splitting too.
>>          */
>> @@ -1822,14 +1831,11 @@ static void __split_huge_page(struct page *page,
>>   * from the hugepage.
>>   * Return 0 if the hugepage is split successfully otherwise return 1.
>>   */
>> -int split_huge_page_to_list(struct page *page, struct list_head *list)
>> +static int split_anon_huge_page(struct page *page, struct list_head
>> *list)
>>  {
>>         struct anon_vma *anon_vma;
>>         int ret = 1;
>>
>> -       BUG_ON(is_huge_zero_page(page));
>> -       BUG_ON(!PageAnon(page));
>> -
>>         /*
>>          * The caller does not necessarily hold an mmap_sem that would
>> prevent
>>          * the anon_vma disappearing so we first we take a reference to it
>> @@ -1847,7 +1853,7 @@ int split_huge_page_to_list(struct page *page,
>> struct list_head *list)
>>                 goto out_unlock;
>>
>>         BUG_ON(!PageSwapBacked(page));
>> -       __split_huge_page(page, anon_vma, list);
>> +       __split_anon_huge_page(page, anon_vma, list);
>>         count_vm_event(THP_SPLIT);
>>
>>         BUG_ON(PageCompound(page));
>> @@ -1858,6 +1864,63 @@ out:
>>         return ret;
>>  }
>>
>> +static int split_file_huge_page(struct page *page, struct list_head
>> *list)
>> +{
>> +       struct address_space *mapping = page->mapping;
>> +       pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
>> +       struct vm_area_struct *vma;
>> +       int mapcount, mapcount2;
>> +
>> +       BUG_ON(!PageHead(page));
>> +       BUG_ON(PageTail(page));
>> +
>> +       mutex_lock(&mapping->i_mmap_mutex);
>> +       mapcount = 0;
>> +       vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
>> +               unsigned long addr = vma_address(page, vma);
>> +               mapcount += __split_huge_page_splitting(page, vma, addr);
>> +       }
>> +
>> +       if (mapcount != page_mapcount(page))
>> +               printk(KERN_ERR "mapcount %d page_mapcount %d\n",
>> +                      mapcount, page_mapcount(page));
>> +       BUG_ON(mapcount != page_mapcount(page));
>> +
>> +       __split_huge_page_refcount(page, list);
>> +
>> +       mapcount2 = 0;
>> +       vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
>> +               unsigned long addr = vma_address(page, vma);
>> +               mapcount2 += __split_huge_page_map(page, vma, addr);
>> +       }
>> +
>> +       if (mapcount != mapcount2)
>> +               printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount
>> %d\n",
>> +                      mapcount, mapcount2, page_mapcount(page));
>> +       BUG_ON(mapcount != mapcount2);
>> +       count_vm_event(THP_SPLIT);
>> +       mutex_unlock(&mapping->i_mmap_mutex);
>> +
>> +       /*
>> +        * Drop small pages beyond i_size if any.
>> +        *
>> +        * XXX: do we need to serialize over i_mutex here?
>> +        * If yes, how to get mmap_sem vs. i_mutex ordering fixed?
>> +        */
>> +       truncate_inode_pages(mapping, i_size_read(mapping->host));
>> +       return 0;
>> +}
>> +
>> +int split_huge_page_to_list(struct page *page, struct list_head *list)
>> +{
>> +       BUG_ON(is_huge_zero_page(page));
>> +
>> +       if (PageAnon(page))
>> +               return split_anon_huge_page(page, list);
>> +       else
>> +               return split_file_huge_page(page, list);
>> +}
>> +
>>  #define VM_NO_THP
>> (VM_SPECIAL|VM_MIXEDMAP|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
>>
>>  int hugepage_madvise(struct vm_area_struct *vma,
>> --
>> 1.8.3.2
>>
>>
>

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