From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id E31EF8D0039 for ; Wed, 9 Feb 2011 15:06:28 -0500 (EST) Date: Wed, 9 Feb 2011 12:05:50 -0800 From: Andrew Morton Subject: Re: [patch] vmscan: fix zone shrinking exit when scan work is done Message-Id: <20110209120550.2bd18590.akpm@linux-foundation.org> In-Reply-To: <20110209182846.GN3347@random.random> References: <20110209154606.GJ27110@cmpxchg.org> <20110209164656.GA1063@csn.ul.ie> <20110209182846.GN3347@random.random> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrea Arcangeli Cc: Mel Gorman , Johannes Weiner , Rik van Riel , Michal Hocko , Kent Overstreet , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, 9 Feb 2011 19:28:46 +0100 Andrea Arcangeli wrote: > On Wed, Feb 09, 2011 at 04:46:56PM +0000, Mel Gorman wrote: > > On Wed, Feb 09, 2011 at 04:46:06PM +0100, Johannes Weiner wrote: > > > Hi, > > > > > > I think this should fix the problem of processes getting stuck in > > > reclaim that has been reported several times. > > > > I don't think it's the only source but I'm basing this on seeing > > constant looping in balance_pgdat() and calling congestion_wait() a few > > weeks ago that I haven't rechecked since. However, this looks like a > > real fix for a real problem. > > Agreed. Just yesterday I spent some time on the lumpy compaction > changes after wondering about Michal's khugepaged 100% report, and I > expected some fix was needed in this area (as I couldn't find any bug > in khugepaged yet, so the lumpy compaction looked the next candidate > for bugs). > > I've also been wondering about the !nr_scanned check in > should_continue_reclaim too but I didn't look too much into the caller > (I was tempted to remove it all together). I don't see how checking > nr_scanned can be safe even after we fix the caller to avoid passing > non-zero values if "goto restart". > > nr_scanned is incremented even for !page_evictable... so it's not > really useful to insist, just because we scanned something, in my > view. It looks bogus... So my proposal would be below. > > ==== > Subject: mm: stop checking nr_scanned in should_continue_reclaim > > From: Andrea Arcangeli > > nr_scanned is incremented even for !page_evictable... so it's not > really useful to insist, just because we scanned something. So if reclaim has scanned 100% !page_evictable pages, should_continue_reclaim() can return true and we keep on scanning? That sounds like it's both good and bad :( Is this actually a problem? What sort of behaviour could it cause and under what circumstances? Johannes's patch is an obvious bugfix and I'll run with it for now, but please let's have a further think abut the impact of the !page_evictable pages. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org