From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wj0-f199.google.com (mail-wj0-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id 7A4596B0033 for ; Thu, 26 Jan 2017 12:47:51 -0500 (EST) Received: by mail-wj0-f199.google.com with SMTP id an2so41135825wjc.3 for ; Thu, 26 Jan 2017 09:47:51 -0800 (PST) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id 1si2815558wrh.309.2017.01.26.09.47.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 26 Jan 2017 09:47:49 -0800 (PST) Date: Thu, 26 Jan 2017 12:47:39 -0500 From: Johannes Weiner Subject: Re: [PATCH 2/5] mm: vmscan: kick flushers when we encounter dirty pages on the LRU Message-ID: <20170126174739.GA30636@cmpxchg.org> References: <20170123181641.23938-1-hannes@cmpxchg.org> <20170123181641.23938-3-hannes@cmpxchg.org> <20170126095745.ueigbrsop5vgmwzj@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170126095745.ueigbrsop5vgmwzj@suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Thu, Jan 26, 2017 at 09:57:45AM +0000, Mel Gorman wrote: > On Mon, Jan 23, 2017 at 01:16:38PM -0500, Johannes Weiner wrote: > > Memory pressure can put dirty pages at the end of the LRU without > > anybody running into dirty limits. Don't start writing individual > > pages from kswapd while the flushers might be asleep. > > > > Signed-off-by: Johannes Weiner > > I don't understand the motivation for checking the wb_reason name. Maybe > it was easier to eyeball while reading ftraces. The comment about the > flusher not doing its job could also be as simple as the writes took > place and clean pages were reclaimed before dirty_expire was reached. > Not impossible if there was a light writer combined with a heavy reader > or a large number of anonymous faults. The name change was only because try_to_free_pages() wasn't the only function doing this flusher wakeup anymore. I associate that name with direct reclaim rather than reclaim in general, so I figured this makes more sense. No strong feelings either way, but I doubt this will break anything in userspace. The comment on dirty expiration is a good point. Let's add this to the list of reasons why reclaim might run into dirty data. Fixlet below. > Acked-by: Mel Gorman Thanks! ---