The logic controlling the singly-linked list of swap_info_struct entries for all active, i.e. swapon'ed, swap targets is rather complex, because: -it stores the entries in priority order -there is a pointer to the highest priority entry -there is a pointer to the highest priority not-full entry -there is a highest_priority_index variable set outside the swap_lock -swap entries of equal priority should be used equally this complexity leads to bugs such as: https://lkml.org/lkml/2014/2/13/181 where different priority swap targets are incorrectly used equally. That bug probably could be solved with the existing singly-linked lists, but I think it would only add more complexity to the already difficult to understand get_swap_page() swap_list iteration logic. The first patch changes from a singly-linked list to a doubly-linked list using list_heads; the highest_priority_index and related code are removed and get_swap_page() starts each iteration at the highest priority swap_info entry, even if it's full. While this does introduce unnecessary list iteration (i.e. Schlemiel the painter's algorithm) in the case where one or more of the highest priority entries are full, the iteration and manipulation code is much simpler and behaves correctly re: the above bug; and the second patch removes the unnecessary iteration. The second patch adds a new list that contains only swap_info entries that are both active and not full, and a new spinlock to protect it. This allows swap_info entries to be added or removed from the new list immediately as they become full or not full. Dan Streetman (2): swap: change swap_info singly-linked list to list_head swap: use separate priority list for available swap_infos include/linux/swap.h | 8 +-- include/linux/swapfile.h | 2 +- mm/frontswap.c | 13 ++--- mm/swapfile.c | 212 ++++++++++++++++++++++++++++++++++--------------------------------- 4 files changed, 114 insertions(+), 121 deletions(-) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>