Re: [PATCH] mm: swap: Use swapfiles in priority order

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Hi,
first of all I hope this patching in of the Mesage-ID works for threaded 
views :-)

On 13/02/14 10:42:31, Mel Gorman wrote:
 >
 >
 > [prev in list] [next in list] [prev in thread] [next in thread]
 >
 > List:       linux-mm
 > Subject:    [PATCH] mm: swap: Use swapfiles in priority order
 > From:       Mel Gorman <mgorman () suse ! de>
 > Date:       2014-02-13 10:42:31
 > Message-ID: 20140213104231.GX6732 () suse ! de
 > [Download message RAW]
 >
 > According to the swapon documentation
 >
 > 	Swap  pages  are  allocated  from  areas  in priority order,
 > 	highest priority first.  For areas with different priorities, a
 > 	higher-priority area is exhausted before using a lower-priority area.
 >
 > A user reported

That was me and I can confirm that for all my setup were we encountered 
the issue is fixed with the new patch.

On top of that it also fixed a long running issue that swap gets slower 
the more swap targets you have - which was formerly discussed in detail 
here http://www.spinics.net/lists/linux-mm/msg68624.html

 > that the reality is different. When multiple swap files
 > are enabled and a memory consumer started, the swap files are consumed in
 > pairs after the highest priority file is exhausted. Early in the lifetime
 > of the test, swapfile consumptions looks like
 >
[...]
 >
 > Signed-off-by: Mel Gorman <mgorman@suse.de>
 > ---
 >  mm/swapfile.c | 2 +-
 >  1 file changed, 1 insertion(+), 1 deletion(-)
 >
 > diff --git a/mm/swapfile.c b/mm/swapfile.c
 > index 4a7f7e6..6d0ac2b 100644
 > --- a/mm/swapfile.c
 > +++ b/mm/swapfile.c
 > @@ -651,7 +651,7 @@ swp_entry_t get_swap_page(void)
 >  		goto noswap;
 >  	atomic_long_dec(&nr_swap_pages);
 >
 > -	for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
 > +	for (type = swap_list.head; type >= 0 && wrapped < 2; type = next) {
 >  		hp_index = atomic_xchg(&highest_priority_index, -1);
 >  		/*
 >  		 * highest_priority_index records current highest priority swap


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