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Date: Mon, 8 Jun 2009 16:11:51 +0100 From: Mel Gorman <mel@....ul.ie> To: Christoph Lameter <cl@...ux-foundation.org> Cc: Rik van Riel <riel@...hat.com>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, yanmin.zhang@...el.com, Wu Fengguang <fengguang.wu@...el.com>, linuxram@...ibm.com, linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA On Mon, Jun 08, 2009 at 10:55:55AM -0400, Christoph Lameter wrote: > On Mon, 8 Jun 2009, Mel Gorman wrote: > > > > The tmpfs pages are unreclaimable and therefore should not be on the anon > > > lru. > > > > > > > tmpfs pages can be swap-backed so can be reclaimable. Regardless of what > > list they are on, we still need to know how many of them there are if > > this patch is to be avoided. > > If they are reclaimable then why does it matter? They can be pushed out if > you configure zone reclaim to be that aggressive. > Because they are reclaimable by kswapd or normal direct reclaim but *not* reclaimable by zone_reclaim() if the zone_reclaim_mode is not configured appropriately. I briefly considered setting zone_reclaim_mode to 7 instead of 1 by default for large NUMA distances but that has other serious consequences such as paging in preference to going off-node as a default out-of-box behaviour. The point of the patch is that the heuristics that avoid the scan are not perfect. In the event they are wrong and a useless scan occurs, the response of the kernel after a useless scan should not be to uselessly scan a load more times around the LRU lists making no progress. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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