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The goal of this patchset is to make refcounting on THP pages cheaper with simpler semantics and allow the same THP compound page to be mapped with PMD and PTEs. This is required to get reasonable THP-pagecache implementation. With the new refcounting design it's much easier to protect against split_huge_page(): simple reference on a page will make you the deal. It makes gup_fast() implementation simpler and doesn't require special-case in futex code to handle tail THP pages. It should improve THP utilization over the system since splitting THP in one process doesn't necessary lead to splitting the page in all other processes have the page mapped. The patchset drastically lower complexity of get_page()/put_page() codepaths. I encourage people look on this code before-and-after to justify time budget on reviewing this patchset. This patch (of 37): With new refcounting all subpages of the compound page are not necessary have the same mapcount. We need to take into account mapcount of every sub-page. Signed-off-by: Kirill A. Shutemov <[email protected]> Tested-by: Sasha Levin <[email protected]> Tested-by: Aneesh Kumar K.V <[email protected]> Acked-by: Jerome Marchand <[email protected]> Acked-by: Vlastimil Babka <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Naoya Horiguchi <[email protected]> Cc: Steve Capper <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: David Rientjes <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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