On Wed, 27 Apr 2011 17:08:10 +0100 Mel Gorman <mgorman@xxxxxxx> wrote:
> +/*
> + * Throttle direct reclaimers if backing storage is backed by the network
> + * and the PFMEMALLOC reserve for the preferred node is getting dangerously
> + * depleted. kswapd will continue to make progress and wake the processes
> + * when the low watermark is reached
> + */
> +static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
> + nodemask_t *nodemask)
> +{
> + struct zone *zone;
> + int high_zoneidx = gfp_zone(gfp_mask);
> + DEFINE_WAIT(wait);
> +
> + /* Check if the pfmemalloc reserves are ok */
> + first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
> + if (pfmemalloc_watermark_ok(zone->zone_pgdat, high_zoneidx))
> + return;
As the first thing that 'wait_event_interruptible" does is test the condition
and return if it is true, this "if () return;" is pointless.
> +
> + /* Throttle */
> + wait_event_interruptible(zone->zone_pgdat->pfmemalloc_wait,
> + pfmemalloc_watermark_ok(zone->zone_pgdat, high_zoneidx));
> +}
I was surprised that you chose wait_event_interruptible as your previous code
was almost exactly "wait_event_killable".
Is there some justification for not throttling processes which happen to have
a (non-fatal) signal pending?
Thanks,
NeilBrown
> +
> unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> gfp_t gfp_mask, nodemask_t *nodemask)
> {
> @@ -2133,6 +2172,15 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> .nodemask = nodemask,
> };
>
> + throttle_direct_reclaim(gfp_mask, zonelist, nodemask);
> +
> + /*
> + * Do not enter reclaim if fatal signal is pending. 1 is returned so
> + * that the page allocator does not consider triggering OOM
> + */
> + if (fatal_signal_pending(current))
> + return 1;
> +
> trace_mm_vmscan_direct_reclaim_begin(order,
> sc.may_writepage,
> gfp_mask);
> @@ -2488,6 +2536,12 @@ loop_again:
> }
>
> }
> +
> + /* Wake throttled direct reclaimers if low watermark is met */
> + if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
> + pfmemalloc_watermark_ok(pgdat, MAX_NR_ZONES - 1))
> + wake_up_interruptible(&pgdat->pfmemalloc_wait);
> +
> if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
> break; /* kswapd: all done */
> /*
--
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