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Diffstat (limited to 'Documentation/mm/vmemmap_dedup.rst')
| -rw-r--r-- | Documentation/mm/vmemmap_dedup.rst | 22 |
1 files changed, 1 insertions, 21 deletions
diff --git a/Documentation/mm/vmemmap_dedup.rst b/Documentation/mm/vmemmap_dedup.rst index 593ede6d31..b4a55b6569 100644 --- a/Documentation/mm/vmemmap_dedup.rst +++ b/Documentation/mm/vmemmap_dedup.rst @@ -180,27 +180,7 @@ this correctly. There is only **one** head ``struct page``, the tail ``struct page`` with ``PG_head`` are fake head ``struct page``. We need an approach to distinguish between those two different types of ``struct page`` so that ``compound_head()`` can return the real head ``struct page`` when the -parameter is the tail ``struct page`` but with ``PG_head``. The following code -snippet describes how to distinguish between real and fake head ``struct page``. - -.. code-block:: c - - if (test_bit(PG_head, &page->flags)) { - unsigned long head = READ_ONCE(page[1].compound_head); - - if (head & 1) { - if (head == (unsigned long)page + 1) - /* head struct page */ - else - /* tail struct page */ - } else { - /* head struct page */ - } - } - -We can safely access the field of the **page[1]** with ``PG_head`` because the -page is a compound page composed with at least two contiguous pages. -The implementation refers to ``page_fixed_fake_head()``. +parameter is the tail ``struct page`` but with ``PG_head``. Device DAX ========== |