On Fri, Feb 14, 2014 at 6:17 PM, Mel Gorman <[email protected]> wrote: > 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
I am sorry to waste your time, I should have tested it. I will review the code more carefully, and send a tested patch if I find a better way. Apologize again. > 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/
