From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754136AbcHYEo7 (ORCPT ); Thu, 25 Aug 2016 00:44:59 -0400 Received: from mail-pf0-f170.google.com ([209.85.192.170]:32843 "EHLO mail-pf0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751393AbcHYEno (ORCPT ); Thu, 25 Aug 2016 00:43:44 -0400 Date: Wed, 24 Aug 2016 17:54:52 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Michal Hocko cc: Andrew Morton , Mel Gorman , Joonsoo Kim , Vlastimil Babka , Markus Trippelsdorf , linux-mm@kvack.org, LKML , Michal Hocko Subject: Re: [PATCH] mm: clarify COMPACTION Kconfig text In-Reply-To: <1471939757-29789-1-git-send-email-mhocko@kernel.org> Message-ID: References: <1471939757-29789-1-git-send-email-mhocko@kernel.org> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 23 Aug 2016, Michal Hocko wrote: > From: Michal Hocko > > The current wording of the COMPACTION Kconfig help text doesn't > emphasise that disabling COMPACTION might cripple the page allocator > which relies on the compaction quite heavily for high order requests and > an unexpected OOM can happen with the lack of compaction. Make sure > we are vocal about that. > Since when has this been an issue? I don't believe it has been an issue in the past for any archs that don't use thp. > Signed-off-by: Michal Hocko > --- > mm/Kconfig | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/Kconfig b/mm/Kconfig > index 78a23c5c302d..0dff2f05b6d1 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -262,7 +262,14 @@ config COMPACTION > select MIGRATION > depends on MMU > help > - Allows the compaction of memory for the allocation of huge pages. > + Compaction is the only memory management component to form > + high order (larger physically contiguous) memory blocks > + reliably. Page allocator relies on the compaction heavily and > + the lack of the feature can lead to unexpected OOM killer > + invocation for high order memory requests. You shouldnm't > + disable this option unless there is really a strong reason for > + it and then we are really interested to hear about that at > + linux-mm@kvack.org. > > # > # support for page migration This seems to strongly suggest that all kernels should be built with CONFIG_COMPACTION and its requirement, CONFIG_MIGRATION. Migration has a dependency of NUMA or memory hot-remove (not all popular). Compaction can defragment memory within single zone without reliance on NUMA. This seems like a very bizarre requirement and I'm wondering where we regressed from this thp-only behavior. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id E414C6B0269 for ; Wed, 24 Aug 2016 20:54:55 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id o124so62147242pfg.1 for ; Wed, 24 Aug 2016 17:54:55 -0700 (PDT) Received: from mail-pf0-x234.google.com (mail-pf0-x234.google.com. [2607:f8b0:400e:c00::234]) by mx.google.com with ESMTPS id to7si12239083pac.282.2016.08.24.17.54.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Aug 2016 17:54:54 -0700 (PDT) Received: by mail-pf0-x234.google.com with SMTP id y134so11950417pfg.0 for ; Wed, 24 Aug 2016 17:54:54 -0700 (PDT) Date: Wed, 24 Aug 2016 17:54:52 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH] mm: clarify COMPACTION Kconfig text In-Reply-To: <1471939757-29789-1-git-send-email-mhocko@kernel.org> Message-ID: References: <1471939757-29789-1-git-send-email-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Mel Gorman , Joonsoo Kim , Vlastimil Babka , Markus Trippelsdorf , linux-mm@kvack.org, LKML , Michal Hocko On Tue, 23 Aug 2016, Michal Hocko wrote: > From: Michal Hocko > > The current wording of the COMPACTION Kconfig help text doesn't > emphasise that disabling COMPACTION might cripple the page allocator > which relies on the compaction quite heavily for high order requests and > an unexpected OOM can happen with the lack of compaction. Make sure > we are vocal about that. > Since when has this been an issue? I don't believe it has been an issue in the past for any archs that don't use thp. > Signed-off-by: Michal Hocko > --- > mm/Kconfig | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/Kconfig b/mm/Kconfig > index 78a23c5c302d..0dff2f05b6d1 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -262,7 +262,14 @@ config COMPACTION > select MIGRATION > depends on MMU > help > - Allows the compaction of memory for the allocation of huge pages. > + Compaction is the only memory management component to form > + high order (larger physically contiguous) memory blocks > + reliably. Page allocator relies on the compaction heavily and > + the lack of the feature can lead to unexpected OOM killer > + invocation for high order memory requests. You shouldnm't > + disable this option unless there is really a strong reason for > + it and then we are really interested to hear about that at > + linux-mm@kvack.org. > > # > # support for page migration This seems to strongly suggest that all kernels should be built with CONFIG_COMPACTION and its requirement, CONFIG_MIGRATION. Migration has a dependency of NUMA or memory hot-remove (not all popular). Compaction can defragment memory within single zone without reliance on NUMA. This seems like a very bizarre requirement and I'm wondering where we regressed from this thp-only behavior. -- 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