• Dan Streetman's avatar
    lib/plist: add plist_requeue · a75f232c
    Dan Streetman authored
    Add plist_requeue(), which moves the specified plist_node after all other
    same-priority plist_nodes in the list.  This is essentially an optimized
    plist_del() followed by plist_add().
    
    This is needed by swap, which (with the next patch in this set) uses a
    plist of available swap devices.  When a swap device (either a swap
    partition or swap file) are added to the system with swapon(), the device
    is added to a plist, ordered by the swap device's priority.  When swap
    needs to allocate a page from one of the swap devices, it takes the page
    from the first swap device on the plist, which is the highest priority
    swap device.  The swap device is left in the plist until all its pages are
    used, and then removed from the plist when it becomes full.
    
    However, as described in man 2 swapon, swap must allocate pages from swap
    devices with the same priority in round-robin order; to do this, on each
    swap page allocation, swap uses a page from the first swap device in the
    plist, and then calls plist_requeue() to move that swap device entry to
    after any other same-priority swap devices.  The next swap page allocation
    will again use a page from the first swap device in the plist and requeue
    it, and so on, resulting in round-robin usage of equal-priority swap
    devices.
    
    Also add plist_test_requeue() test function, for use by plist_test() to
    test plist_requeue() function.
    Signed-off-by: default avatarDan Streetman <ddstreet@ieee.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Acked-by: default avatarMel Gorman <mgorman@suse.de>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Shaohua Li <shli@fusionio.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Dan Streetman <ddstreet@ieee.org>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
    Cc: Weijie Yang <weijieut@gmail.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Bob Liu <bob.liu@oracle.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    a75f232c
plist.c 5.9 KB