On Thu, Feb 13, 2014 at 6:42 PM, Mel Gorman <mgorman@xxxxxxx> 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 <mgorman@xxxxxxx>
> ---
> 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?
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 4a7f7e6..d64aa55 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -676,7 +676,7 @@ swp_entry_t get_swap_page(void)
next = si->next;
if (next < 0 ||
(!wrapped && si->prio != swap_info[next]->prio)) {
- next = swap_list.head;
+ next = type;
wrapped++;
}
> hp_index = atomic_xchg(&highest_priority_index, -1);
> /*
> * highest_priority_index records current highest priority swap
> --
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