On Thu, Dec 9, 2010 at 8:18 PM, Mel Gorman <mel@xxxxxxxxx> wrote:
> Before kswapd goes to sleep, it uses sleeping_prematurely() to check if
> there was a race pushing a zone below its watermark. If the race
> happened, it stays awake. However, balance_pgdat() can decide to reclaim
> at a lower order if it decides that high-order reclaim is not working as
Could you specify "order-0" explicitly instead of "a lower order"?
It makes more clear to me.
> expected. This information is not passed back to sleeping_prematurely().
> The impact is that kswapd remains awake reclaiming pages long after it
> should have gone to sleep. This patch passes the adjusted order to
> sleeping_prematurely and uses the same logic as balance_pgdat to decide
> if it's ok to go to sleep.
>
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
A comment below.
> ---
> mm/vmscan.c | 14 ++++++++++----
> 1 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b4472a1..52e229e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2132,7 +2132,7 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced)
> }
>
> /* is kswapd sleeping prematurely? */
> -static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
> +static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
> {
> int i;
> unsigned long balanced = 0;
> @@ -2142,7 +2142,7 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
> if (remaining)
> return 1;
>
> - /* If after HZ/10, a zone is below the high mark, it's premature */
> + /* Check the watermark levels */
> for (i = 0; i < pgdat->nr_zones; i++) {
> struct zone *zone = pgdat->node_zones + i;
>
> @@ -2427,7 +2427,13 @@ out:
> }
> }
>
> - return sc.nr_reclaimed;
> + /*
> + * Return the order we were reclaiming at so sleeping_prematurely()
> + * makes a decision on the order we were last reclaiming at. However,
> + * if another caller entered the allocator slow path while kswapd
> + * was awake, order will remain at the higher level
> + */
> + return order;
> }
Please change return value description of balance_pgdat.
"Returns the number of pages which were actually freed"
--
Kind regards,
Minchan Kim
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