On Wed, 2013-01-09 at 22:41 +0100, Zlatko Calusic wrote:
> From: Zlatko Calusic <zlatko.calusic@xxxxxxxx>
>
> Currently we take a short nap (HZ/10) and wait for congestion to clear
> before taking another pass with lower priority in balance_pgdat(). But
> we do that only for the highest zone that we encounter is unbalanced
> and congested.
>
> This patch changes that to wait on all congested zones in a single
> pass in the hope that it will save us some scanning that way. Also we
> take a nap as soon as congested zone is encountered and sc.priority <
> DEF_PRIORITY - 2 (aka kswapd in trouble).
But you still didn't explain what's the problem you meat and what
scenario can get benefit from your change.
>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
> Signed-off-by: Zlatko Calusic <zlatko.calusic@xxxxxxxx>
> ---
> The patch is against the mm tree. Make sure that
> mm-avoid-calling-pgdat_balanced-needlessly.patch is applied first (not
> yet in the mmotm tree). Tested on half a dozen systems with different
> workloads for the last few days, working really well!
>
> mm/vmscan.c | 35 ++++++++++++-----------------------
> 1 file changed, 12 insertions(+), 23 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 002ade6..1c5d38a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2565,7 +2565,6 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> int *classzone_idx)
> {
> bool pgdat_is_balanced = false;
> - struct zone *unbalanced_zone;
> int i;
> int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
> unsigned long total_scanned;
> @@ -2596,9 +2595,6 @@ loop_again:
>
> do {
> unsigned long lru_pages = 0;
> - int has_under_min_watermark_zone = 0;
> -
> - unbalanced_zone = NULL;
>
> /*
> * Scan in the highmem->dma direction for the highest
> @@ -2739,15 +2735,20 @@ loop_again:
> }
>
> if (!zone_balanced(zone, testorder, 0, end_zone)) {
> - unbalanced_zone = zone;
> - /*
> - * We are still under min water mark. This
> - * means that we have a GFP_ATOMIC allocation
> - * failure risk. Hurry up!
> - */
> + if (total_scanned && sc.priority < DEF_PRIORITY - 2) {
> + /* OK, kswapd is getting into trouble. */
> if (!zone_watermark_ok_safe(zone, order,
> min_wmark_pages(zone), end_zone, 0))
> - has_under_min_watermark_zone = 1;
> + /*
> + * We are still under min water mark.
> + * This means that we have a GFP_ATOMIC
> + * allocation failure risk. Hurry up!
> + */
> + count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
> + else
> + /* Take a nap if a zone is congested. */
> + wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
> + }
> } else {
> /*
> * If a zone reaches its high watermark,
> @@ -2758,7 +2759,6 @@ loop_again:
> */
> zone_clear_flag(zone, ZONE_CONGESTED);
> }
> -
> }
>
> /*
> @@ -2776,17 +2776,6 @@ loop_again:
> }
>
> /*
> - * OK, kswapd is getting into trouble. Take a nap, then take
> - * another pass across the zones.
> - */
> - if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
> - if (has_under_min_watermark_zone)
> - count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
> - else if (unbalanced_zone)
> - wait_iff_congested(unbalanced_zone, BLK_RW_ASYNC, HZ/10);
> - }
> -
> - /*
> * We do this so kswapd doesn't build up large priorities for
> * example when it is freeing in parallel with allocators. It
> * matches the direct reclaim path behaviour in terms of impact
> --
> 1.8.1
>
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