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From: Michal Hocko <mhocko@kernel.org>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	virtio-dev@lists.oasis-open.org,
	virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Oscar Salvador <osalvador@suse.de>,
	Igor Mammedov <imammedo@redhat.com>,
	Dave Young <dyoung@redhat.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v1 07/11] virtio-mem: Allow to offline partially unplugged memory blocks
Date: Tue, 10 Mar 2020 12:59:55 +0100	[thread overview]
Message-ID: <20200310115955.GI8447@dhcp22.suse.cz> (raw)
In-Reply-To: <e505b4cb-1d12-d6e6-3524-9dfa65ae34bf@redhat.com>

On Tue 10-03-20 12:46:05, David Hildenbrand wrote:
> On 10.03.20 12:43, Michal Hocko wrote:
> > On Mon 02-03-20 14:49:37, David Hildenbrand wrote:
> > [...]
> >> +static void virtio_mem_notify_going_offline(struct virtio_mem *vm,
> >> +					    unsigned long mb_id)
> >> +{
> >> +	const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
> >> +	unsigned long pfn;
> >> +	int sb_id, i;
> >> +
> >> +	for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
> >> +		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
> >> +			continue;
> >> +		/*
> >> +		 * Drop our reference to the pages so the memory can get
> >> +		 * offlined and add the unplugged pages to the managed
> >> +		 * page counters (so offlining code can correctly subtract
> >> +		 * them again).
> >> +		 */
> >> +		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
> >> +			       sb_id * vm->subblock_size);
> >> +		adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
> >> +		for (i = 0; i < nr_pages; i++)
> >> +			page_ref_dec(pfn_to_page(pfn + i));
> > 
> > Is there ever situation this might be a different than 1->0 transition?
> 
> Only if some other code would be taking a reference. At least not from
> virtio-mem perspective.

OK, so that is essentially an error condition. I think it shouldn't go
silent and you want something like
	if (WARN_ON(!page_ref_sub_and_test(page)))
		dump_page(pfn_to_page(pfn + i), "YOUR REASON");

-- 
Michal Hocko
SUSE Labs


  reply	other threads:[~2020-03-10 11:59 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-02 13:49 [PATCH v1 00/11] virtio-mem: paravirtualized memory David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 01/11] ACPI: NUMA: export pxm_to_node David Hildenbrand
2020-03-02 14:03   ` Michal Hocko
2020-03-02 14:09     ` David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 02/11] virtio-mem: Paravirtualized memory hotplug David Hildenbrand
2020-03-03  2:24   ` kbuild test robot
2020-03-03  8:06     ` David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 03/11] virtio-mem: Paravirtualized memory hotunplug part 1 David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 04/11] mm: Export alloc_contig_range() / free_contig_range() David Hildenbrand
2020-03-02 14:05   ` Michal Hocko
2020-03-02 14:17     ` David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 05/11] virtio-mem: Paravirtualized memory hotunplug part 2 David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 06/11] mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE David Hildenbrand
2020-03-02 17:40   ` Alexander Duyck
2020-03-02 18:41     ` David Hildenbrand
2020-03-10 11:47   ` Michal Hocko
2020-03-10 11:48     ` David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 07/11] virtio-mem: Allow to offline partially unplugged memory blocks David Hildenbrand
2020-03-10 11:43   ` Michal Hocko
2020-03-10 11:46     ` David Hildenbrand
2020-03-10 11:59       ` Michal Hocko [this message]
2020-03-10 12:09         ` David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 08/11] mm/memory_hotplug: Introduce offline_and_remove_memory() David Hildenbrand
2020-03-02 14:27   ` Michal Hocko
2020-03-02 13:49 ` [PATCH v1 09/11] virtio-mem: Offline and remove completely unplugged memory blocks David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 10/11] virtio-mem: Better retry handling David Hildenbrand
2020-03-02 13:49 ` [PATCH v1 11/11] MAINTAINERS: Add myself as virtio-mem maintainer David Hildenbrand
2020-03-02 18:15 ` [PATCH v1 00/11] virtio-mem: paravirtualized memory David Hildenbrand
2020-03-02 18:29   ` Michal Hocko
2020-03-02 18:41     ` David Hildenbrand

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