On Thu, Feb 13, 2014 at 11:58:05PM +0800, Weijie Yang wrote: > On Thu, Feb 13, 2014 at 6:42 PM, Mel Gorman <[email protected]> wrote: > > 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 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 > > > > Filename Type Size Used > > Priority > > /testswap1 file 100004 100004 8 > > /testswap2 file 100004 23764 7 > > /testswap3 file 100004 23764 6 > > /testswap4 file 100004 0 5 > > /testswap5 file 100004 0 4 > > /testswap6 file 100004 0 3 > > /testswap7 file 100004 0 2 > > /testswap8 file 100004 0 1 > > > > This patch fixes the swap_list search in get_swap_page to use the swap files > > in the correct order. When applied the swap file consumptions looks like > > > > Filename Type Size Used > > Priority > > /testswap1 file 100004 100004 8 > > /testswap2 file 100004 100004 7 > > /testswap3 file 100004 29372 6 > > /testswap4 file 100004 0 5 > > /testswap5 file 100004 0 4 > > /testswap6 file 100004 0 3 > > /testswap7 file 100004 0 2 > > /testswap8 file 100004 0 1 > > > > Signed-off-by: Mel Gorman <[email protected]> > > --- > > 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) { > > Does it lead to a "schlemiel the painter's algorithm"? > (please forgive my rude words, but I can't find a precise word to describe it > because English is not my native language. My apologize.) > > How about modify it like this? >
I blindly applied your version without review to see how it behaved and found it uses every second swapfile like this Filename Type Size Used Priority /testswap1 file 100004 100004 8 /testswap2 file 100004 16 7 /testswap3 file 100004 100004 6 /testswap4 file 100004 8 5 /testswap5 file 100004 100004 4 /testswap6 file 100004 8 3 /testswap7 file 100004 100004 2 /testswap8 file 100004 23504 1 I admit I did not review the swap priority search algorithm in detail because the fix superficially looked straight forward but this alternative is not the answer either. -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
