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From: Wei Yang <richard.weiyang@linux.alibaba.com>
To: David Hildenbrand <david@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	virtualization@lists.linux-foundation.org,
	Andrew Morton <akpm@linux-foundation.org>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Subject: Re: [PATCH v1 05/29] virtio-mem: generalize check for added memory
Date: Sat, 17 Oct 2020 06:38:11 +0800	[thread overview]
Message-ID: <20201016223811.GJ44269@L-31X9LVDL-1304.local> (raw)
In-Reply-To: <be3dca3d-f5e1-c2d6-460b-04e666619db8@redhat.com>

On Fri, Oct 16, 2020 at 12:32:50PM +0200, David Hildenbrand wrote:
>>>> Ok, I seems to understand the logic now.
>>>>
>>>> But how we prevent ONLINE_PARTIAL memory block get offlined? There are three
>>>> calls in virtio_mem_set_fake_offline(), while all of them adjust page's flag.
>>>> How they hold reference to struct page?
>>>
>>> Sorry, I should have given you the right pointer. (similar to my other
>>> reply)
>>>
>>> We hold a reference either via
>>>
>>> 1. alloc_contig_range()
>> 
>> I am not familiar with this one, need to spend some time to look into.
>
>Each individual page will have a pagecount of 1.
>
>> 
>>> 2. memmap init code, when not calling generic_online_page().
>> 
>> I may miss some code here. Before online pages, memmaps are allocated in
>> section_activate(). They are supposed to be zero-ed. (I don't get the exact
>> code line.) I am not sure when we grab a refcount here.
>
>Best to refer to __init_single_page() -> init_page_count().
>
>Each page that wasn't onlined via generic_online_page() has a refcount
>of 1 and looks like allocated.
>

Thanks, I see the logic.

    online_pages()
        move_pfn_range_to_zone()  --- 1)
	online_pages_range()      --- 2)

At 1), __init_single_page() would set page count to 1. At 2),
generic_online_page() would clear page count, while the call back would not.

Then I am trying to search the place where un-zero page count prevent offline.
scan_movable_pages() would fail, since this is a PageOffline() and has 1 page
count.

So the GUARD we prevent offline partial-onlined pages is

    (PageOffline && page_count)

And your commit aa218795cb5fd583c94f

mm: Allow to offline unmovable PageOffline() pages via MEM_GOING_OFFLINE

is introduced to handle this case.

That's pretty clear now.

>-- 
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me

  reply	other threads:[~2020-10-16 22:38 UTC|newest]

Thread overview: 108+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 12:52 [PATCH v1 00/29] virtio-mem: Big Block Mode (BBM) David Hildenbrand
2020-10-12 12:52 ` [PATCH v1 01/29] virtio-mem: determine nid only once using memory_add_physaddr_to_nid() David Hildenbrand
2020-10-15  3:56   ` Wei Yang
2020-10-15 19:26   ` Pankaj Gupta
2020-10-12 12:52 ` [PATCH v1 02/29] virtio-mem: simplify calculation in virtio_mem_mb_state_prepare_next_mb() David Hildenbrand
2020-10-15  4:02   ` Wei Yang
2020-10-15  8:00     ` David Hildenbrand
2020-10-15 10:00       ` Wei Yang
2020-10-15 10:01         ` David Hildenbrand
2020-10-15 20:24   ` Pankaj Gupta
2020-10-16  9:00     ` David Hildenbrand
2020-10-12 12:52 ` [PATCH v1 03/29] virtio-mem: simplify MAX_ORDER - 1 / pageblock_order handling David Hildenbrand
2020-10-15  7:06   ` Wei Yang
2020-10-12 12:52 ` [PATCH v1 04/29] virtio-mem: drop rc2 in virtio_mem_mb_plug_and_add() David Hildenbrand
2020-10-12 13:09   ` Pankaj Gupta
2020-10-15  7:14   ` Wei Yang
2020-10-12 12:52 ` [PATCH v1 05/29] virtio-mem: generalize check for added memory David Hildenbrand
2020-10-15  8:28   ` Wei Yang
2020-10-15  8:50     ` David Hildenbrand
2020-10-16  2:16       ` Wei Yang
2020-10-16  9:11         ` David Hildenbrand
2020-10-16 10:02           ` Wei Yang
2020-10-16 10:32             ` David Hildenbrand
2020-10-16 22:38               ` Wei Yang [this message]
2020-10-17  7:39                 ` David Hildenbrand
2020-10-18 12:27                   ` Wei Yang
2020-10-16 22:39   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 06/29] virtio-mem: generalize virtio_mem_owned_mb() David Hildenbrand
2020-10-15  8:32   ` Wei Yang
2020-10-15  8:37     ` David Hildenbrand
2020-10-15 20:30   ` Pankaj Gupta
2020-10-12 12:53 ` [PATCH v1 07/29] virtio-mem: generalize virtio_mem_overlaps_range() David Hildenbrand
2020-10-20  9:22   ` Pankaj Gupta
2020-10-12 12:53 ` [PATCH v1 08/29] virtio-mem: drop last_mb_id David Hildenbrand
2020-10-15  8:35   ` Wei Yang
2020-10-15 20:32   ` Pankaj Gupta
2020-10-12 12:53 ` [PATCH v1 09/29] virtio-mem: don't always trigger the workqueue when offlining memory David Hildenbrand
2020-10-16  4:03   ` Wei Yang
2020-10-16  9:18     ` David Hildenbrand
2020-10-18  3:57       ` Wei Yang
2020-10-19  9:04         ` David Hildenbrand
2020-10-20  0:41           ` Wei Yang
2020-10-20  9:09             ` David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 10/29] virtio-mem: generalize handling when memory is getting onlined deferred David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 11/29] virtio-mem: use "unsigned long" for nr_pages when fake onlining/offlining David Hildenbrand
2020-10-15 20:31   ` Pankaj Gupta
2020-10-16  6:11   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 12/29] virtio-mem: factor out fake-offlining into virtio_mem_fake_offline() David Hildenbrand
2020-10-16  6:24   ` Wei Yang
2020-10-20  9:31   ` Pankaj Gupta
2020-10-12 12:53 ` [PATCH v1 13/29] virtio-mem: factor out handling of fake-offline pages in memory notifier David Hildenbrand
2020-10-16  7:15   ` Wei Yang
2020-10-16  8:00     ` Wei Yang
2020-10-16  8:57       ` David Hildenbrand
2020-10-18 12:37         ` Wei Yang
2020-10-18 12:38   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 14/29] virtio-mem: retry fake-offlining via alloc_contig_range() on ZONE_MOVABLE David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 15/29] virito-mem: document Sub Block Mode (SBM) David Hildenbrand
2020-10-15  9:33   ` David Hildenbrand
2020-10-20  9:38     ` Pankaj Gupta
2020-10-16  8:03   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 16/29] virtio-mem: memory block states are specific to " David Hildenbrand
2020-10-16  8:40   ` Wei Yang
2020-10-16  8:43   ` Wei Yang
2020-10-20  9:48   ` Pankaj Gupta
2020-10-12 12:53 ` [PATCH v1 17/29] virito-mem: subblock " David Hildenbrand
2020-10-16  8:43   ` Wei Yang
2020-10-20  9:54   ` Pankaj Gupta
2020-10-12 12:53 ` [PATCH v1 18/29] virtio-mem: factor out calculation of the bit number within the sb_states bitmap David Hildenbrand
2020-10-16  8:46   ` Wei Yang
2020-10-20  9:58   ` Pankaj Gupta
2020-10-12 12:53 ` [PATCH v1 19/29] virito-mem: existing (un)plug functions are specific to Sub Block Mode (SBM) David Hildenbrand
2020-10-16  8:49   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 20/29] virtio-mem: nb_sb_per_mb and subblock_size " David Hildenbrand
2020-10-16  8:51   ` Wei Yang
2020-10-16  8:53   ` Wei Yang
2020-10-16 13:17     ` David Hildenbrand
2020-10-18 12:41       ` Wei Yang
2020-10-19 11:57         ` David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 21/29] virtio-mem: memory notifier callbacks " David Hildenbrand
2020-10-19  1:57   ` Wei Yang
2020-10-19 10:22     ` David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 22/29] virtio-mem: memory block ids " David Hildenbrand
2020-10-16  8:54   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 23/29] virtio-mem: factor out adding/removing memory from Linux David Hildenbrand
2020-10-16  8:59   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 24/29] virtio-mem: print debug messages from virtio_mem_send_*_request() David Hildenbrand
2020-10-16  9:07   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 25/29] virtio-mem: Big Block Mode (BBM) memory hotplug David Hildenbrand
2020-10-16  9:38   ` Wei Yang
2020-10-16 13:13     ` David Hildenbrand
2020-10-19  2:26   ` Wei Yang
2020-10-19  9:15     ` David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 26/29] virtio-mem: allow to force Big Block Mode (BBM) and set the big block size David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 27/29] mm/memory_hotplug: extend offline_and_remove_memory() to handle more than one memory block David Hildenbrand
2020-10-15 13:08   ` Michael S. Tsirkin
2020-10-19  3:22   ` Wei Yang
2020-10-12 12:53 ` [PATCH v1 28/29] virtio-mem: Big Block Mode (BBM) - basic memory hotunplug David Hildenbrand
2020-10-19  3:48   ` Wei Yang
2020-10-19  9:12     ` David Hildenbrand
2020-10-12 12:53 ` [PATCH v1 29/29] virtio-mem: Big Block Mode (BBM) - safe " David Hildenbrand
2020-10-19  7:54   ` Wei Yang
2020-10-19  8:50     ` David Hildenbrand
2020-10-20  0:23       ` Wei Yang
2020-10-20  0:24   ` Wei Yang
2020-10-18 12:49 ` [PATCH v1 00/29] virtio-mem: Big Block Mode (BBM) Wei Yang
2020-10-18 15:29 ` Michael S. Tsirkin
2020-10-18 16:34   ` David Hildenbrand

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