Messages in this thread Patch in this message | | | Date | Thu, 28 Apr 2011 10:22:44 +1000 | From | NeilBrown <> | Subject | Re: [PATCH 12/13] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage |
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On Wed, 27 Apr 2011 17:08:10 +0100 Mel Gorman <mgorman@suse.de> 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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