Re: [PATCHv2 3/4] plist: add plist_requeue

[Mel Gorman]

On Mon, May 12, 2014 at 12:38:19PM -0400, Dan Streetman wrote:
> 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: Dan Streetman <ddstreet@xxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> 

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs
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