From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753879AbcFPJIm (ORCPT ); Thu, 16 Jun 2016 05:08:42 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35947 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751323AbcFPJIi (ORCPT ); Thu, 16 Jun 2016 05:08:38 -0400 Date: Thu, 16 Jun 2016 12:08:20 +0300 From: Ebru Akagunduz To: Minchan Kim , mhocko@suse.cz, linux-mm@kvack.org Cc: hughd@google.com, riel@redhat.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, iamjoonsoo.kim@lge.com, gorcunov@openvz.org, linux-kernel@vger.kernel.org, mgorman@suse.de, rientjes@google.com, vbabka@suse.cz, aneesh.kumar@linux.vnet.ibm.com, hannes@cmpxchg.org, mhocko@suse.cz, boaz@plexistor.com Subject: Re: [RFC PATCH 2/3] mm, thp: convert from optimistic to conservative Message-ID: <20160616090819.GA18977@gezgin> References: <1465672561-29608-1-git-send-email-ebru.akagunduz@gmail.com> <1465672561-29608-3-git-send-email-ebru.akagunduz@gmail.com> <20160615064053.GH17127@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160615064053.GH17127@bbox> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 15, 2016 at 03:40:53PM +0900, Minchan Kim wrote: > Hello, > > On Sat, Jun 11, 2016 at 10:16:00PM +0300, Ebru Akagunduz wrote: > > Currently, khugepaged collapses pages saying only > > a referenced page enough to create a THP. > > > > This patch changes the design from optimistic to conservative. > > It gives a default threshold which is half of HPAGE_PMD_NR > > for referenced pages, also introduces a new sysfs knob. > > Strictly speaking, It's not what I suggested. > > I didn't mean that let's change threshold for deciding whether we should > collapse or not(although just *a* reference page seems be too > optimistic) and export the knob to the user. In fact, I cannot judge > whether it's worth or not because I never have an experience with THP > workload in practice although I believe it does make sense. > > What I suggested is that a swapin operation would be much heavier than > a THP cost to collapse populated anon page so it should be more > conservative than THP collasping decision, at least. Given that thought, > decision point for collasping a THP is *a* reference page now so *half* > reference of populated pages for reading swapped-out page is more > conservative. > Then passing referenced parameter from khugepaged_scan_pmd to collapse_huge_page_swapin seems okay. A referenced is enough to create THP, if needs to swapin, we check the value that should be higher than 256 and so that, we don't need a new sysfs knob. > > > > Signed-off-by: Ebru Akagunduz > > --- > > +static unsigned int khugepaged_min_ptes_young __read_mostly; > > We should set it to 1 to preserve old behavior.