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Date: Thu, 23 Apr 2009 09:11:18 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: David Rientjes <rientjes@...gle.com> Cc: kosaki.motohiro@...fujitsu.com, Lee Schermerhorn <Lee.Schermerhorn@...com>, Mel Gorman <mel@....ul.ie>, Linux Memory Management List <linux-mm@...ck.org>, Christoph Lameter <cl@...ux-foundation.org>, Nick Piggin <npiggin@...e.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Lin Ming <ming.m.lin@...el.com>, Zhang Yanmin <yanmin_zhang@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, Pekka Enberg <penberg@...helsinki.fi>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH 16/22] Do not setup zonelist cache when there is only one node > On Wed, 22 Apr 2009, Lee Schermerhorn wrote: > > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > > index 7f45de1..e59bb80 100644 > > > > --- a/mm/page_alloc.c > > > > +++ b/mm/page_alloc.c > > > > @@ -1467,8 +1467,11 @@ this_zone_full: > > > > if (NUMA_BUILD) > > > > zlc_mark_zone_full(zonelist, z); > > > > > > If zonelist caching is never used for UMA machines, why should they ever > > > call zlc_mark_zone_full()? It will always dereference > > > zonelist->zlcache_ptr and immediately return without doing anything. > > > > > > Wouldn't it better to just add > > > > > > if (num_online_nodes() == 1) > > > continue; > > > > > > right before this call to zlc_mark_zone_full()? This should compile out > > > the remainder of the loop for !CONFIG_NUMA kernels anyway. > > > > Shouldn't it already do that? NUMA_BUILD is defined as 0 when > > !CONFIG_NUMA to avoid #ifdef's in the code while still allowing compiler > > error checking in the dead code. > > > > Yeah, but adding the check on num_online_nodes() also prevents needlessly > calling zlc_mark_zone_full() on CONFIG_NUMA kernels when running on an UMA > machine. I don't like this idea... In UMA system, zlc_mark_zone_full() isn't so expensive. but In large system one branch increasing is often costly. -- 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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