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 162B86B01F0 for ; Sun, 29 Aug 2010 13:45:24 -0400 (EDT) Received: from kpbe15.cbf.corp.google.com (kpbe15.cbf.corp.google.com [172.25.105.79]) by smtp-out.google.com with ESMTP id o7THjIV4014153 for ; Sun, 29 Aug 2010 10:45:18 -0700 Received: from qyk5 (qyk5.prod.google.com [10.241.83.133]) by kpbe15.cbf.corp.google.com with ESMTP id o7THjGmo025350 for ; Sun, 29 Aug 2010 10:45:16 -0700 Received: by qyk5 with SMTP id 5so2720365qyk.18 for ; Sun, 29 Aug 2010 10:45:16 -0700 (PDT) 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , Venkatesh Pallipadi , Rik van Riel , KOSAKI Motohiro , Johannes Weiner List-ID: 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 lon= g > time. It means many of pages in there would mark access bit again. So acc= ess > 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 > --- > =A0mm/vmscan.c | =A0 =A02 +- > =A01 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: > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 * Do some background agin= g of the anon list, to give > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 * pages a chance to be re= ferenced before reclaiming. > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 */ > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (inactive_anon_is_low(zo= ne, &sc)) > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (total_swap_pages > 0 &&= inactive_anon_is_low(zone, &sc)) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0shrink_act= ive_list(SWAP_CLUSTER_MAX, zone, > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 = =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0&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, 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