From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 3FDE86B0055 for ; Wed, 10 Jun 2009 01:22:55 -0400 (EDT) Date: Tue, 9 Jun 2009 22:23:01 -0700 From: Andrew Morton Subject: Re: [PATCH 1/3] Reintroduce zone_reclaim_interval for when zone_reclaim() scans and fails to avoid CPU spinning at 100% on NUMA Message-Id: <20090609222301.8da002ae.akpm@linux-foundation.org> In-Reply-To: <20090608151151.GI15070@csn.ul.ie> References: <1244466090-10711-1-git-send-email-mel@csn.ul.ie> <1244466090-10711-2-git-send-email-mel@csn.ul.ie> <4A2D129D.3020309@redhat.com> <20090608135433.GD15070@csn.ul.ie> <20090608143857.GG15070@csn.ul.ie> <20090608151151.GI15070@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Christoph Lameter , Rik van Riel , KOSAKI Motohiro , yanmin.zhang@intel.com, Wu Fengguang , linuxram@us.ibm.com, linux-mm , LKML List-ID: On Mon, 8 Jun 2009 16:11:51 +0100 Mel Gorman wrote: > 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. Ah. (zone_reclaim_mode & RECLAIM_SWAP) == 0. That was important info. Couldn't the lack of RECLAIM_WRITE cause a similar problem? > 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. Maybe we should consider that a bit harder. At what stage does zone_reclaim decide to give up and try a different node? Perhaps it's presently too reluctant to do that? > 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. It would be sad to bring back a jiffies-based thing into page reclaim. Wall time has little correlation with the rate of page allocation and reclaim activity. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org