From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f198.google.com (mail-qt0-f198.google.com [209.85.216.198]) by kanga.kvack.org (Postfix) with ESMTP id 44A106B0005 for ; Fri, 20 Apr 2018 03:30:40 -0400 (EDT) Received: by mail-qt0-f198.google.com with SMTP id f13-v6so5389573qtg.15 for ; Fri, 20 Apr 2018 00:30:40 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id 13si7361658qkv.7.2018.04.20.00.30.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 20 Apr 2018 00:30:39 -0700 (PDT) Subject: Re: [PATCH RFC 2/8] mm: introduce PG_offline References: <20180413131632.1413-1-david@redhat.com> <20180413131632.1413-3-david@redhat.com> From: David Hildenbrand Message-ID: <6624ec31-0b18-62dc-bcc3-5f8a2bf8da49@redhat.com> Date: Fri, 20 Apr 2018 09:30:26 +0200 MIME-Version: 1.0 In-Reply-To: <20180413131632.1413-3-david@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: Steven Rostedt , Ingo Molnar , Andrew Morton , Michal Hocko , Huang Ying , Greg Kroah-Hartman , Pavel Tatashin , Miles Chen , Vlastimil Babka , Mel Gorman , Rik van Riel , James Hogan , "Levin, Alexander (Sasha Levin)" , open list On 13.04.2018 15:16, David Hildenbrand wrote: > online_pages()/offline_pages() theoretically allows us to work on > sub-section sizes. This is especially relevant in the context of > virtualization. It e.g. allows us to add/remove memory to Linux in a VM in > 4MB chunks. > > While the whole section is marked as online/offline, we have to know > the state of each page. E.g. to not read memory that is not online > during kexec() or to properly mark a section as offline as soon as all > contained pages are offline. > > Signed-off-by: David Hildenbrand > --- > include/linux/page-flags.h | 10 ++++++++++ > include/trace/events/mmflags.h | 9 ++++++++- > 2 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index e34a27727b9a..8ebc4bad7824 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -49,6 +49,9 @@ > * PG_hwpoison indicates that a page got corrupted in hardware and contains > * data with incorrect ECC bits that triggered a machine check. Accessing is > * not safe since it may cause another machine check. Don't touch! > + * > + * PG_offline indicates that a page is offline and the backing storage > + * might already have been removed (virtualization). Don't touch! > */ > > /* > @@ -100,6 +103,9 @@ enum pageflags { > #if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT) > PG_young, > PG_idle, > +#endif > +#ifdef CONFIG_MEMORY_HOTPLUG > + PG_offline, /* Page is offline. Don't touch */ > #endif > __NR_PAGEFLAGS, > > @@ -381,6 +387,10 @@ TESTCLEARFLAG(Young, young, PF_ANY) > PAGEFLAG(Idle, idle, PF_ANY) > #endif > > +#ifdef CONFIG_MEMORY_HOTPLUG > +PAGEFLAG(Offline, offline, PF_ANY) > +#endif > + > /* > * On an anonymous page mapped into a user virtual memory area, > * page->mapping points to its anon_vma, not to a struct address_space; > diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h > index a81cffb76d89..14c31209e34a 100644 > --- a/include/trace/events/mmflags.h > +++ b/include/trace/events/mmflags.h > @@ -79,6 +79,12 @@ > #define IF_HAVE_PG_IDLE(flag,string) > #endif > > +#ifdef CONFIG_MEMORY_HOTPLUG > +#define IF_HAVE_PG_OFFLINE(flag,string) ,{1UL << flag, string} > +#else > +#define IF_HAVE_PG_OFFLINE(flag,string) > +#endif > + > #define __def_pageflag_names \ > {1UL << PG_locked, "locked" }, \ > {1UL << PG_waiters, "waiters" }, \ > @@ -104,7 +110,8 @@ IF_HAVE_PG_MLOCK(PG_mlocked, "mlocked" ) \ > IF_HAVE_PG_UNCACHED(PG_uncached, "uncached" ) \ > IF_HAVE_PG_HWPOISON(PG_hwpoison, "hwpoison" ) \ > IF_HAVE_PG_IDLE(PG_young, "young" ) \ > -IF_HAVE_PG_IDLE(PG_idle, "idle" ) > +IF_HAVE_PG_IDLE(PG_idle, "idle" ) \ > +IF_HAVE_PG_OFFLINE(PG_offline, "offline" ) > > #define show_page_flags(flags) \ > (flags) ? __print_flags(flags, "|", \ > I am thinking right now of gluing this to CONFIG_MEMORY_PG_OFFLINE and allowing it to be used also for ordinary balloon drivers. It is then basically a way to signal using kdump "don't dump this page, the content is either invalid or not even accessible". -- Thanks, David / dhildenb