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    thp: split_huge_page paging · 3f04f62f
    Andrea Arcangeli 提交于
    Paging logic that splits the page before it is unmapped and added to swap
    to ensure backwards compatibility with the legacy swap code.  Eventually
    swap should natively pageout the hugepages to increase performance and
    decrease seeking and fragmentation of swap space.  swapoff can just skip
    over huge pmd as they cannot be part of swap yet.  In add_to_swap be
    careful to split the page only if we got a valid swap entry so we don't
    split hugepages with a full swap.
    
    In theory we could split pages before isolating them during the lru scan,
    but for khugepaged to be safe, I'm relying on either mmap_sem write mode,
    or PG_lock taken, so split_huge_page has to run either with mmap_sem
    read/write mode or PG_lock taken.  Calling it from isolate_lru_page would
    make locking more complicated, in addition to that split_huge_page would
    deadlock if called by __isolate_lru_page because it has to take the lru
    lock to add the tail pages.
    Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
    Acked-by: NMel Gorman <mel@csn.ul.ie>
    Acked-by: NRik van Riel <riel@redhat.com>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    3f04f62f
swapfile.c 65.5 KB