Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753919Ab0H2RpU (ORCPT ); Sun, 29 Aug 2010 13:45:20 -0400 Received: from smtp-out.google.com ([216.239.44.51]:9128 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753888Ab0H2RpT convert rfc822-to-8bit (ORCPT ); Sun, 29 Aug 2010 13:45:19 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=x6A2Mh8UlG094VBF1whfxp/kZtx5WII8FhevJR4VCTn0P4KLr+pmBk9uNJYk4Sripu RVN2RlZ6SKmi8k8VoOdw== MIME-Version: 1.0 In-Reply-To: <1283096628-4450-1-git-send-email-minchan.kim@gmail.com> References: <1283096628-4450-1-git-send-email-minchan.kim@gmail.com> Date: Sun, 29 Aug 2010 10:45:15 -0700 Message-ID: Subject: Re: [PATCH] vmscan: prevent background aging of anon page in no swap system From: Ying Han To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , Venkatesh Pallipadi , Rik van Riel , KOSAKI Motohiro , Johannes Weiner Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3275 Lines: 80 On Sun, Aug 29, 2010 at 8:43 AM, Minchan Kim wrote: > Ying Han reported that backing aging of anon pages in no swap system > causes unnecessary TLB flush. > > When I sent a patch(69c8548175), I wanted this patch but Rik pointed out > and allowed aging of anon pages to give a chance to promote from inactive > to active LRU. > > It has a two problem. > > 1) non-swap system > > Never make sense to age anon pages. > > 2) swap configured but still doesn't swapon > > It doesn't make sense to age anon pages until swap-on time. > But it's arguable. If we have aged anon pages by swapon, VM have moved > anon pages from active to inactive. And in the time swapon by admin, > the VM can't reclaim hot pages so we can protect hot pages swapout. > > But let's think about it. When does swap-on happen? It depends on admin. > we can't expect it. Nonetheless, we have done aging of anon pages to > protect hot pages swapout. It means we lost run time overhead when > below high watermark but gain hot page swap-[in/out] overhead when VM > decide swapout. Is it true? Let's think more detail. > We don't promote anon pages in case of non-swap system. So even though > VM does aging of anon pages, the pages would be in inactive LRU for a long > time. It means many of pages in there would mark access bit again. So access > bit hot/code separation would be pointless. > > This patch prevents unnecessary anon pages demotion in not-swapon and > non-configured swap system. Of course, it could make side effect that > hot anon pages could swap out when admin does swap on. > But I think sooner or later it would be steady state. > So it's not a big problem. > We could lose someting but gain more thing(TLB flush and unnecessary > function call to demote anon pages). > > I used total_swap_pages because we want to age anon pages > even though swap full happens. > > Cc: Rik van Riel > Cc: KOSAKI Motohiro > Cc: Johannes Weiner > Reported-by: Ying Han > Signed-off-by: Minchan Kim > --- > ?mm/vmscan.c | ? ?2 +- > ?1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 3109ff7..d8fd87d 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2211,7 +2211,7 @@ loop_again: > ? ? ? ? ? ? ? ? ? ? ? ? * Do some background aging of the anon list, to give > ? ? ? ? ? ? ? ? ? ? ? ? * pages a chance to be referenced before reclaiming. > ? ? ? ? ? ? ? ? ? ? ? ? */ > - ? ? ? ? ? ? ? ? ? ? ? if (inactive_anon_is_low(zone, &sc)) > + ? ? ? ? ? ? ? ? ? ? ? if (total_swap_pages > 0 && inactive_anon_is_low(zone, &sc)) > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?shrink_active_list(SWAP_CLUSTER_MAX, zone, > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?&sc, priority, 0); > > -- > 1.7.0.5 > > There are few other places in vmscan where we check nr_swap_pages and inactive_anon_is_low. Are we planning to change them to use total_swap_pages to be consistent ? --Ying -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/