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    [PATCH] swap: swap_lock replace list+device · 5d337b91
    Hugh Dickins 提交于
    The idea of a swap_device_lock per device, and a swap_list_lock over them all,
    is appealing; but in practice almost every holder of swap_device_lock must
    already hold swap_list_lock, which defeats the purpose of the split.
    
    The only exceptions have been swap_duplicate, valid_swaphandles and an
    untrodden path in try_to_unuse (plus a few places added in this series).
    valid_swaphandles doesn't show up high in profiles, but swap_duplicate does
    demand attention.  However, with the hold time in get_swap_pages so much
    reduced, I've not yet found a load and set of swap device priorities to show
    even swap_duplicate benefitting from the split.  Certainly the split is mere
    overhead in the common case of a single swap device.
    
    So, replace swap_list_lock and swap_device_lock by spinlock_t swap_lock
    (generally we seem to prefer an _ in the name, and not hide in a macro).
    
    If someone can show a regression in swap_duplicate, then probably we should
    add a hashlock for the swap_map entries alone (shorts being anatomic), so as
    to help the case of the single swap device too.
    Signed-off-by: NHugh Dickins <hugh@veritas.com>
    Signed-off-by: NAndrew Morton <akpm@osdl.org>
    Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
    5d337b91
swapfile.c 41.9 KB