From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6252C4646A for ; Wed, 12 Sep 2018 14:21:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87CA020880 for ; Wed, 12 Sep 2018 14:21:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87CA020880 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726860AbeILT0M (ORCPT ); Wed, 12 Sep 2018 15:26:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:43758 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726537AbeILT0M (ORCPT ); Wed, 12 Sep 2018 15:26:12 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 8C1F9AD18; Wed, 12 Sep 2018 14:21:27 +0000 (UTC) Date: Wed, 12 Sep 2018 16:21:26 +0200 From: Michal Hocko To: Andrea Arcangeli Cc: David Rientjes , Andrew Morton , Zi Yan , "Kirill A. Shutemov" , linux-mm@kvack.org, LKML , Stefan Priebe Subject: Re: [PATCH] mm, thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings Message-ID: <20180912142126.GM10951@dhcp22.suse.cz> References: <20180907130550.11885-1-mhocko@kernel.org> <20180911115613.GR10951@dhcp22.suse.cz> <20180912135417.GA15194@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180912135417.GA15194@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 12-09-18 09:54:17, Andrea Arcangeli wrote: > Hello, > > On Tue, Sep 11, 2018 at 01:56:13PM +0200, Michal Hocko wrote: > > Well, it seems that expectations differ for users. It seems that kvm > > users do not really agree with your interpretation. > > Like David also mentioned here: > > lkml.kernel.org/r/alpine.DEB.2.21.1808211021110.258924@chino.kir.corp.google.com > > depends on the hardware what is a win, so there's no one size fits > all. > > For two sockets providing remote THP to KVM is likely a win, but > changing the defaults depending on boot-time NUMA topology makes > things less deterministic and it's also impossible to define an exact > break even point. > > > I do realize that this is a gray zone because nobody bothered to define > > the semantic since the MADV_HUGEPAGE has been introduced (a826e422420b4 > > is exceptionaly short of information). So we are left with more or less > > undefined behavior and define it properly now. As we can see this might > > regress in some workloads but I strongly suspect that an explicit > > binding sounds more logical approach than a thp specific mpol mode. If > > anything this should be a more generic memory policy basically saying > > that a zone/node reclaim mode should be enabled for the particular > > allocation. > > MADV_HUGEPAGE means the allocation is long lived, so the cost of > compaction is worth it in direct reclaim. Not much else. That is not > the problem. It seems there is no general agreement here. My understanding is that this means that the user really prefers THP for whatever reasons. > The problem is that even if you ignore the breakage and regression to > real life workloads, what is happening right now obviously would > require root privilege but MADV_HUEGPAGE requires no root privilege. I do not follow. > Swapping heavy because MADV_HUGEPAGE when there are gigabytes free on > other nodes and not even 4k would be swapped-out with THP turned off > in sysfs, is simply not possibly what MADV_HUGEPAGE could have been > about, and it's a kernel regression that never existed until that > commit that added __GFP_THISNODE to the default THP heuristic in > mempolicy. agreed > I think we should defer the problem of what is better between 4k NUMA > local or remote THP by default for later, I provided two options > myself because it didn't matter so much which option we picked in the > short term, as long as the bug was fixed. > > I wasn't particularly happy about your patch because it still swaps > with certain defrag settings which is still allowing things that > shouldn't happen without some kind of privileged capability. Well, I am not really sure about defrag=always. I would rather care about the default behavior to plug the regression first. And think about `always' mode on top. Or is this a no-go from your POV? -- Michal Hocko SUSE Labs