From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 60FA86B1BB3 for ; Mon, 19 Nov 2018 12:33:15 -0500 (EST) Received: by mail-ed1-f72.google.com with SMTP id o42so16228084edc.13 for ; Mon, 19 Nov 2018 09:33:15 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id y20si2677634edb.128.2018.11.19.09.33.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 19 Nov 2018 09:33:14 -0800 (PST) Date: Mon, 19 Nov 2018 18:33:12 +0100 From: Michal Hocko Subject: Re: Memory hotplug softlock issue Message-ID: <20181119173312.GV22247@dhcp22.suse.cz> References: <20181115131211.GP2653@MiWiFi-R3L-srv> <20181115131927.GT23831@dhcp22.suse.cz> <20181115133840.GR2653@MiWiFi-R3L-srv> <20181115143204.GV23831@dhcp22.suse.cz> <20181116012433.GU2653@MiWiFi-R3L-srv> <20181116091409.GD14706@dhcp22.suse.cz> <20181119105202.GE18471@MiWiFi-R3L-srv> <20181119124033.GJ22247@dhcp22.suse.cz> <20181119125121.GK22247@dhcp22.suse.cz> <20181119141016.GO22247@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181119141016.GO22247@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Baoquan He Cc: David Hildenbrand , linux-mm@kvack.org, pifang@redhat.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, aarcange@redhat.com, Mel Gorman , Vlastimil Babka , Hugh Dickins On Mon 19-11-18 15:10:16, Michal Hocko wrote: [...] > In other words. Why cannot we do the following? Baoquan, this is certainly not the right fix but I would be really curious whether it makes the problem go away. > diff --git a/mm/migrate.c b/mm/migrate.c > index f7e4bfdc13b7..7ccab29bcf9a 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -324,19 +324,9 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep, > goto out; > > page = migration_entry_to_page(entry); > - > - /* > - * Once page cache replacement of page migration started, page_count > - * *must* be zero. And, we don't want to call wait_on_page_locked() > - * against a page without get_page(). > - * So, we use get_page_unless_zero(), here. Even failed, page fault > - * will occur again. > - */ > - if (!get_page_unless_zero(page)) > - goto out; > pte_unmap_unlock(ptep, ptl); > - wait_on_page_locked(page); > - put_page(page); > + page_lock(page); > + page_unlock(page); > return; > out: > pte_unmap_unlock(ptep, ptl); -- Michal Hocko SUSE Labs