On 06/07/2013 08:10 AM, Kirill A. Shutemov wrote:
> + /*
> + * 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.
> + */
> + init_tail_refcount = PageAnon(page) ? 0 : 1;
What's the "init" for in the name?
In add_to_page_cache_locked() in patch 12/39, you do
> + spin_lock_irq(&mapping->tree_lock);
> + for (i = 0; i < nr; i++) {
> + page_cache_get(page + i);
That looks to me to be taking references to the tail pages. What gives? :)
> for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
> struct page *page_tail = page + i;
>
> @@ -1587,8 +1595,9 @@ 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(init_tail_refcount + page_mapcount(page) +
> + page_mapcount(page_tail) + 1,
> + &page_tail->_count);
>
> /* after clearing PageTail the gup refcount can be released */
> smp_mb();
This does look much better in general, though.
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