This second iteration of this patchset adds two more patches, to add functions to plist; those are the 2nd and 3rd patches. The first patch is unchanged functionally, it only has added/modified comments. The last patch is changed to use plists instead of regular lists, as it did before. 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 fourth patch removes the unnecessary iteration. The second patch adds some minor plist helper functions; nothing new really, just functions to match existing regular list functions. These are used by the next two patches. The third patch adds plist_rotate(), which is used by get_swap_page() in the next patch - it performs the rotating of same-priority entries so that all equal-priority swap_info_structs get used equally. The fourth patch converts the main list into a plist, and adds a new plist that contains only swap_info entries that are both active and not full. As Mel suggested using plists allows removing all the ordering code from swap - plists handle ordering automatically. The list naming is also clarified now that there are two lists, with the original list changed from swap_list_head to swap_active_head and the new list named swap_avail_head. A new spinlock is also added for the new list, so swap_info entries can be added or removed from the new list immediately as they become full or not full. Dan Streetman (4): swap: change swap_info singly-linked list to list_head plist: add helper functions plist: add plist_rotate swap: change swap_list_head to plist, add swap_avail_head include/linux/plist.h | 45 ++++++++++ include/linux/swap.h | 8 +- include/linux/swapfile.h | 2 +- lib/plist.c | 48 ++++++++++ mm/frontswap.c | 13 +-- mm/swapfile.c | 223 ++++++++++++++++++++++++----------------------- 6 files changed, 215 insertions(+), 124 deletions(-) -- 1.8.3.1 -- 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>