From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id 0923E6B01F1 for ; Thu, 19 Aug 2010 06:38:55 -0400 (EDT) Date: Thu, 19 Aug 2010 11:38:39 +0100 From: Mel Gorman Subject: Re: [PATCH 2/3] mm: page allocator: Calculate a better estimate of NR_FREE_PAGES when memory is low and kswapd is awake Message-ID: <20100819103839.GZ19797@csn.ul.ie> References: <1281951733-29466-1-git-send-email-mel@csn.ul.ie> <1281951733-29466-3-git-send-email-mel@csn.ul.ie> <20100816094350.GH19797@csn.ul.ie> <20100816160623.GB15103@cmpxchg.org> <20100817101655.GN19797@csn.ul.ie> <20100817142040.GA3884@barrios-desktop> <20100818085123.GU19797@csn.ul.ie> <20100818145725.GA5744@barrios-desktop> <20100819080624.GX19797@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: Johannes Weiner , linux-mm@kvack.org, Rik van Riel , Nick Piggin , KAMEZAWA Hiroyuki , KOSAKI Motohiro List-ID: On Thu, Aug 19, 2010 at 07:33:57PM +0900, Minchan Kim wrote: > On Thu, Aug 19, 2010 at 5:06 PM, Mel Gorman wrote: > > On Wed, Aug 18, 2010 at 11:57:26PM +0900, Minchan Kim wrote: > >> On Wed, Aug 18, 2010 at 09:51:23AM +0100, Mel Gorman wrote: > >> > > What's a window low and min wmark? Maybe I can miss your point. > >> > > > >> > > >> > The window is due to the fact kswapd is not awake yet. The window is because > >> > kswapd might not be awake as NR_FREE_PAGES is higher than it should be. The > >> > system is really somewhere between the low and min watermark but we are not > >> > taking the accurate measure until kswapd gets woken up. The first allocation > >> > to notice we are below the low watermark (be it due to vmstat refreshing or > >> > that NR_FREE_PAGES happens to report we are below the watermark regardless of > >> > any drift) wakes kswapd and other callers then take an accurate count hence > >> > "we could breach the watermark but I'm expecting it can only happen for at > >> > worst one allocation". > >> > >> Right. I misunderstood your word. > >> One more question. > >> > >> Could you explain live lock scenario? > >> > > > > Lets say > > > > NR_FREE_PAGES = 256 > > Actual free pages = 8 > > > > The PCP lists get refilled in patch taking all 8 pages. Now there are > > zero free pages. Reclaim kicks in but to reclaim any pages it needs to > > clean something but all the pages are on a network-backed filesystem. To > > clean them, it must transmit on the network so it tries to allocate some > > buffers. > > > > The livelock is that to free some memory, an allocation must succeed but > > for an allocation to succeed, some memory must be freed. The system > > Yes. I understood this as livelock but at last VM will kill victim > process then it can allocate free pages. And if the exit path for the OOM kill needs to allocate a page what should it do? > So I think it's not a livelock. > > > might still remain alive if a process exits and does not need to > > allocate memory while exiting but by and large, the system is in a > > dangerous state. > > Do you mean dangerous state of the system is livelock? > Maybe not. > I can't understand livelock in this context. > Anyway, I am okay with this patch except livelock pharse. :) > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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