From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 9F3386B029E for ; Wed, 22 Nov 2017 09:53:09 -0500 (EST) Received: by mail-wm0-f72.google.com with SMTP id n8so3196948wmg.4 for ; Wed, 22 Nov 2017 06:53:09 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v15si5963192edm.114.2017.11.22.06.53.08 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 22 Nov 2017 06:53:08 -0800 (PST) Date: Wed, 22 Nov 2017 15:53:07 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: migrate: fix an incorrect call of prep_transhuge_page() Message-ID: <20171122145307.52klaq4ouorngsss@dhcp22.suse.cz> References: <20171121021855.50525-1-zi.yan@sent.com> <20171122085416.ycrvahu2bznlx37s@dhcp22.suse.cz> <20171122134059.fmyambktkel4e3zq@dhcp22.suse.cz> <5A158D22.3040609@cs.rutgers.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5A158D22.3040609@cs.rutgers.edu> Sender: owner-linux-mm@kvack.org List-ID: To: Zi Yan Cc: Zi Yan , Naoya Horiguchi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrea Reale , =?iso-8859-1?B?Suly9G1l?= Glisse , stable@vger.kernel.org On Wed 22-11-17 09:43:46, Zi Yan wrote: > > > Michal Hocko wrote: > > On Wed 22-11-17 09:54:16, Michal Hocko wrote: > >> On Mon 20-11-17 21:18:55, Zi Yan wrote: > > [...] > >>> diff --git a/include/linux/migrate.h b/include/linux/migrate.h > >>> index 895ec0c4942e..a2246cf670ba 100644 > >>> --- a/include/linux/migrate.h > >>> +++ b/include/linux/migrate.h > >>> @@ -54,7 +54,7 @@ static inline struct page *new_page_nodemask(struct page *page, > >>> new_page = __alloc_pages_nodemask(gfp_mask, order, > >>> preferred_nid, nodemask); > >>> > >>> - if (new_page && PageTransHuge(page)) > >>> + if (new_page && PageTransHuge(new_page)) > >>> prep_transhuge_page(new_page); > >> I would keep the two checks consistent. But that leads to a more > >> interesting question. new_page_nodemask does > >> > >> if (thp_migration_supported() && PageTransHuge(page)) { > >> order = HPAGE_PMD_ORDER; > >> gfp_mask |= GFP_TRANSHUGE; > >> } > > > > And one more question/note. Why do we need thp_migration_supported > > in the first place? 9c670ea37947 ("mm: thp: introduce > > CONFIG_ARCH_ENABLE_THP_MIGRATION") says > > : Introduce CONFIG_ARCH_ENABLE_THP_MIGRATION to limit thp migration > > : functionality to x86_64, which should be safer at the first step. > > > > but why is unsafe to enable the feature on other arches which support > > THP? Is there any plan to do the next step and remove this config > > option? > > Because different architectures have their own way of specifying a swap > entry. This means, to support THP migration, each architecture needs to > add its own __pmd_to_swp_entry() and __swp_entry_to_pmd(), which are > used for arch-independent pmd_to_swp_entry() and swp_entry_to_pmd(). I understand that part. But this smells like a matter of coding, no? I was suprised to see the note about safety which didn't make much sense to me. -- 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