From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 61B246B1C4D for ; Mon, 19 Nov 2018 15:59:10 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id k58so27558eda.20 for ; Mon, 19 Nov 2018 12:59:10 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id g17-v6si4414991ejm.318.2018.11.19.12.59.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 19 Nov 2018 12:59:08 -0800 (PST) Date: Mon, 19 Nov 2018 21:59:07 +0100 From: Michal Hocko Subject: Re: Memory hotplug softlock issue Message-ID: <20181119205907.GW22247@dhcp22.suse.cz> References: <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> <20181119173312.GV22247@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Baoquan He , 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 On Mon 19-11-18 12:34:09, Hugh Dickins wrote: > On Mon, 19 Nov 2018, Michal Hocko wrote: > > 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); > > Thanks for Cc'ing me. I did mention precisely this issue two or three > times at LSF/MM this year, and claimed then that I would post the fix. I've had a recollection about some issue I just couldn't remember what was it exactly. Tried to make Vlastimil to remember but failed there as well ;) > I'm glad that I delayed, what I had then (migration_waitqueue instead > of using page_waitqueue) was not wrong, but what I've been using the > last couple of months is rather better (and can be put to use to solve > similar problems in collapsing pages on huge tmpfs. but we don't need > to get into that at this time): put_and_wait_on_page_locked(). > > What I have not yet done is verify it on latest kernel, and research > the interested Cc list (Linus and Tim Chen come immediately to mind), > and write the commit comment. I have some testing to do on the latest > kernel today, so I'll throw put_and_wait_on_page_locked() in too, > and post tomorrow I hope. Cool, it seems that Baoquan has a reliable test case to trigger the pathological case. -- Michal Hocko SUSE Labs