From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id EC0126B0033 for ; Sun, 5 Feb 2017 05:11:19 -0500 (EST) Received: by mail-wm0-f69.google.com with SMTP id q124so14513977wmg.2 for ; Sun, 05 Feb 2017 02:11:19 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id c15si37899130wrd.188.2017.02.05.02.11.18 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sun, 05 Feb 2017 02:11:18 -0800 (PST) Date: Sun, 5 Feb 2017 11:11:14 +0100 From: Michal Hocko Subject: Re: [PATCH] mm, vmscan: Clear PGDAT_WRITEBACK when zone is balanced Message-ID: <20170205101113.GB22713@dhcp22.suse.cz> References: <20170203203222.gq7hk66yc36lpgtb@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170203203222.gq7hk66yc36lpgtb@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: 'Andrew Morton' , Hillf Danton , 'Johannes Weiner' , 'Minchan Kim' , 'Rik van Riel' , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri 03-02-17 20:32:22, Mel Gorman wrote: > Hillf Danton pointed out that since commit 1d82de618dd ("mm, vmscan: > make kswapd reclaim in terms of nodes") that PGDAT_WRITEBACK is no longer > cleared. It was not noticed as triggering it requires pages under writeback > to cycle twice through the LRU and before kswapd gets stalled. Historically, > such issues tended to occur on small machines writing heavily to slow > storage such as a USB stick. Once kswapd stalls, direct reclaim stalls may > be higher but due to the fact that memory pressure is requires, it would not > be very noticable. Michal Hocko suggested removing the flag entirely but > the conservative fix is to restore the intended PGDAT_WRITEBACK behaviour > and clear the flag when a suitable zone is balanced. > > Signed-off-by: Mel Gorman I agree this is a more conservative approach but I think removing PGDAT_WRITEBACK should simplify things a bit. Acked-by: Michal Hocko > --- > mm/vmscan.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 532a2a750952..3379fa5ce6d8 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3103,6 +3103,7 @@ static bool zone_balanced(struct zone *zone, int order, int classzone_idx) > */ > clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags); > clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags); > + clear_bit(PGDAT_WRITEBACK, &zone->zone_pgdat->flags); > > return true; > } > > -- > Mel Gorman > SUSE Labs -- Michal Hocko SUSE Labs -- 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