From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-2.mimecast.com ([207.211.31.81]:44696 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726481AbgD2Ozu (ORCPT ); Wed, 29 Apr 2020 10:55:50 -0400 Subject: Re: [PATCH v2] s390: simplify memory notifier for protecting kdump crash kernel area References: <20200424083904.8587-1-david@redhat.com> From: David Hildenbrand Message-ID: <1d79310d-8909-73e7-d2dd-90e8b9edf253@redhat.com> Date: Wed, 29 Apr 2020 16:55:38 +0200 MIME-Version: 1.0 In-Reply-To: <20200424083904.8587-1-david@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-s390@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Martin Schwidefsky , Philipp Rudo , Gerald Schaefer , "Eric W . Biederman" , Michal Hocko On 24.04.20 10:39, David Hildenbrand wrote: > Assume we have a crashkernel area of 256MB reserved: > > root@vm0:~# cat /proc/iomem > 00000000-6fffffff : System RAM > 0f258000-0fcfffff : Kernel code > 0fd00000-101d10e3 : Kernel data > 105b3000-1068dfff : Kernel bss > 70000000-7fffffff : Crash kernel > > This exactly corresponds to memory block 7 (memory block size is 256MB). > Trying to offline that memory block results in: > > root@vm0:~# echo "offline" > /sys/devices/system/memory/memory7/state > -bash: echo: write error: Device or resource busy > > [ 128.458762] page:000003d081c00000 refcount:1 mapcount:0 mapping:00000000d01cecd4 index:0x0 > [ 128.458773] flags: 0x1ffff00000001000(reserved) > [ 128.458781] raw: 1ffff00000001000 000003d081c00008 000003d081c00008 0000000000000000 > [ 128.458781] raw: 0000000000000000 0000000000000000 ffffffff00000001 0000000000000000 > [ 128.458783] page dumped because: unmovable page > > The craskernel area is marked reserved in the bootmem allocator. This > results in the memmap getting initialized (refcount=1, PG_reserved), but > the pages are never freed to the page allocator. > > So these pages look like allocated pages that are unmovable (esp. > PG_reserved), and therefore, memory offlining fails early, when trying to > isolate the page range. > > We only have to care about the exchange area, make that clear. > > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Christian Borntraeger > Cc: Martin Schwidefsky > Cc: Philipp Rudo > Cc: Gerald Schaefer > Cc: Eric W. Biederman > Cc: Michal Hocko > Signed-off-by: David Hildenbrand > --- > > Follow up of: > - "[PATCH v1] s390: drop memory notifier for protecting kdump crash kernel > area" > > v1 -> v2: > - Keep the notifier, check for exchange area only > > --- > arch/s390/kernel/setup.c | 13 +++++-------- > 1 file changed, 5 insertions(+), 8 deletions(-) > > diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c > index 0f0b140b5558..c0881f0a3175 100644 > --- a/arch/s390/kernel/setup.c > +++ b/arch/s390/kernel/setup.c > @@ -594,9 +594,10 @@ static void __init setup_memory_end(void) > #ifdef CONFIG_CRASH_DUMP > > /* > - * When kdump is enabled, we have to ensure that no memory from > - * the area [0 - crashkernel memory size] and > - * [crashk_res.start - crashk_res.end] is set offline. > + * When kdump is enabled, we have to ensure that no memory from the area > + * [0 - crashkernel memory size] is set offline - it will be exchanged with > + * the crashkernel memory region when kdump is triggered. The crashkernel > + * memory region can never get offlined (pages are unmovable). > */ > static int kdump_mem_notifier(struct notifier_block *nb, > unsigned long action, void *data) > @@ -607,11 +608,7 @@ static int kdump_mem_notifier(struct notifier_block *nb, > return NOTIFY_OK; > if (arg->start_pfn < PFN_DOWN(resource_size(&crashk_res))) > return NOTIFY_BAD; > - if (arg->start_pfn > PFN_DOWN(crashk_res.end)) > - return NOTIFY_OK; > - if (arg->start_pfn + arg->nr_pages - 1 < PFN_DOWN(crashk_res.start)) > - return NOTIFY_OK; > - return NOTIFY_BAD; > + return NOTIFY_OK; > } > > static struct notifier_block kdump_mem_nb = { > Ping. -- Thanks, David / dhildenb