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Message-ID: <20201015090815-mutt-send-email-mst@kernel.org>
Date: Thu, 15 Oct 2020 09:08:52 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
virtualization@...ts.linux-foundation.org,
Andrew Morton <akpm@...ux-foundation.org>,
Jason Wang <jasowang@...hat.com>,
Pankaj Gupta <pankaj.gupta.linux@...il.com>,
Michal Hocko <mhocko@...nel.org>,
Oscar Salvador <osalvador@...e.de>,
Wei Yang <richard.weiyang@...ux.alibaba.com>
Subject: Re: [PATCH v1 27/29] mm/memory_hotplug: extend
offline_and_remove_memory() to handle more than one memory block
On Mon, Oct 12, 2020 at 02:53:21PM +0200, David Hildenbrand wrote:
> virtio-mem soon wants to use offline_and_remove_memory() memory that
> exceeds a single Linux memory block (memory_block_size_bytes()). Let's
> remove that restriction.
>
> Let's remember the old state and try to restore that if anything goes
> wrong. While re-onlining can, in general, fail, it's highly unlikely to
> happen (usually only when a notifier fails to allocate memory, and these
> are rather rare).
>
> This will be used by virtio-mem to offline+remove memory ranges that are
> bigger than a single memory block - for example, with a device block
> size of 1 GiB (e.g., gigantic pages in the hypervisor) and a Linux memory
> block size of 128MB.
>
> While we could compress the state into 2 bit, using 8 bit is much
> easier.
>
> This handling is similar, but different to acpi_scan_try_to_offline():
>
> a) We don't try to offline twice. I am not sure if this CONFIG_MEMCG
> optimization is still relevant - it should only apply to ZONE_NORMAL
> (where we have no guarantees). If relevant, we can always add it.
>
> b) acpi_scan_try_to_offline() simply onlines all memory in case
> something goes wrong. It doesn't restore previous online type. Let's do
> that, so we won't overwrite what e.g., user space configured.
>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Jason Wang <jasowang@...hat.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: David Hildenbrand <david@...hat.com>
Could I get some acks from mm folks for this one?
The rest can go in through my tree I guess ...
Andrew?
Thanks!
> ---
> mm/memory_hotplug.c | 105 +++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 89 insertions(+), 16 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b44d4c7ba73b..217080ca93e5 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1806,39 +1806,112 @@ int remove_memory(int nid, u64 start, u64 size)
> }
> EXPORT_SYMBOL_GPL(remove_memory);
>
> +static int try_offline_memory_block(struct memory_block *mem, void *arg)
> +{
> + uint8_t online_type = MMOP_ONLINE_KERNEL;
> + uint8_t **online_types = arg;
> + struct page *page;
> + int rc;
> +
> + /*
> + * Sense the online_type via the zone of the memory block. Offlining
> + * with multiple zones within one memory block will be rejected
> + * by offlining code ... so we don't care about that.
> + */
> + page = pfn_to_online_page(section_nr_to_pfn(mem->start_section_nr));
> + if (page && zone_idx(page_zone(page)) == ZONE_MOVABLE)
> + online_type = MMOP_ONLINE_MOVABLE;
> +
> + rc = device_offline(&mem->dev);
> + /*
> + * Default is MMOP_OFFLINE - change it only if offlining succeeded,
> + * so try_reonline_memory_block() can do the right thing.
> + */
> + if (!rc)
> + **online_types = online_type;
> +
> + (*online_types)++;
> + /* Ignore if already offline. */
> + return rc < 0 ? rc : 0;
> +}
> +
> +static int try_reonline_memory_block(struct memory_block *mem, void *arg)
> +{
> + uint8_t **online_types = arg;
> + int rc;
> +
> + if (**online_types != MMOP_OFFLINE) {
> + mem->online_type = **online_types;
> + rc = device_online(&mem->dev);
> + if (rc < 0)
> + pr_warn("%s: Failed to re-online memory: %d",
> + __func__, rc);
> + }
> +
> + /* Continue processing all remaining memory blocks. */
> + (*online_types)++;
> + return 0;
> +}
> +
> /*
> - * Try to offline and remove a memory block. Might take a long time to
> - * finish in case memory is still in use. Primarily useful for memory devices
> - * that logically unplugged all memory (so it's no longer in use) and want to
> - * offline + remove the memory block.
> + * Try to offline and remove memory. Might take a long time to finish in case
> + * memory is still in use. Primarily useful for memory devices that logically
> + * unplugged all memory (so it's no longer in use) and want to offline + remove
> + * that memory.
> */
> int offline_and_remove_memory(int nid, u64 start, u64 size)
> {
> - struct memory_block *mem;
> - int rc = -EINVAL;
> + const unsigned long mb_count = size / memory_block_size_bytes();
> + uint8_t *online_types, *tmp;
> + int rc;
>
> if (!IS_ALIGNED(start, memory_block_size_bytes()) ||
> - size != memory_block_size_bytes())
> - return rc;
> + !IS_ALIGNED(size, memory_block_size_bytes()) || !size)
> + return -EINVAL;
> +
> + /*
> + * We'll remember the old online type of each memory block, so we can
> + * try to revert whatever we did when offlining one memory block fails
> + * after offlining some others succeeded.
> + */
> + online_types = kmalloc_array(mb_count, sizeof(*online_types),
> + GFP_KERNEL);
> + if (!online_types)
> + return -ENOMEM;
> + /*
> + * Initialize all states to MMOP_OFFLINE, so when we abort processing in
> + * try_offline_memory_block(), we'll skip all unprocessed blocks in
> + * try_reonline_memory_block().
> + */
> + memset(online_types, MMOP_OFFLINE, mb_count);
>
> lock_device_hotplug();
> - mem = find_memory_block(__pfn_to_section(PFN_DOWN(start)));
> - if (mem)
> - rc = device_offline(&mem->dev);
> - /* Ignore if the device is already offline. */
> - if (rc > 0)
> - rc = 0;
> +
> + tmp = online_types;
> + rc = walk_memory_blocks(start, size, &tmp, try_offline_memory_block);
>
> /*
> - * In case we succeeded to offline the memory block, remove it.
> + * In case we succeeded to offline all memory, remove it.
> * This cannot fail as it cannot get onlined in the meantime.
> */
> if (!rc) {
> rc = try_remove_memory(nid, start, size);
> - WARN_ON_ONCE(rc);
> + if (rc)
> + pr_err("%s: Failed to remove memory: %d", __func__, rc);
> + }
> +
> + /*
> + * Rollback what we did. While memory onlining might theoretically fail
> + * (nacked by a notifier), it barely ever happens.
> + */
> + if (rc) {
> + tmp = online_types;
> + walk_memory_blocks(start, size, &tmp,
> + try_reonline_memory_block);
> }
> unlock_device_hotplug();
>
> + kfree(online_types);
> return rc;
> }
> EXPORT_SYMBOL_GPL(offline_and_remove_memory);
> --
> 2.26.2
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