Messages in this thread | | | Date | Mon, 19 Jun 2023 09:41:16 +0200 | Subject | Re: [PATCH stable 5.10] mm/memory_hotplug: extend offline_and_remove_memory() to handle more than one memory block | From | David Hildenbrand <> |
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On 19.06.23 09:22, mawupeng wrote: > > > On 2023/6/19 15:16, Greg KH wrote: >> On Mon, Jun 19, 2023 at 02:51:21PM +0800, Wupeng Ma wrote: >>> From: David Hildenbrand <david@redhat.com> >>> >>> commit 8dc4bb58a146655eb057247d7c9d19e73928715b upstream. >>> >>> 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. >>> >>> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com> >>> Cc: "Michael S. Tsirkin" <mst@redhat.com> >>> Cc: Jason Wang <jasowang@redhat.com> >>> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com> >>> Cc: Michal Hocko <mhocko@kernel.org> >>> Cc: Oscar Salvador <osalvador@suse.de> >>> Cc: Wei Yang <richard.weiyang@linux.alibaba.com> >>> Cc: Andrew Morton <akpm@linux-foundation.org> >>> Signed-off-by: David Hildenbrand <david@redhat.com> >>> Link: https://lore.kernel.org/r/20201112133815.13332-28-david@redhat.com >>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> >>> Acked-by: Andrew Morton <akpm@linux-foundation.org> >>> Signed-off-by: Ma Wupeng <mawupeng1@huawei.com> >>> --- >>> mm/memory_hotplug.c | 105 +++++++++++++++++++++++++++++++++++++------- >>> 1 file changed, 89 insertions(+), 16 deletions(-) >>> >> >> Why is this needed in 5.10.y? Looks like a new feature to me, what >> problem does it solve there? >> >> thanks, >> >> greg k-h > > It do introduce a new feature. But at the same time, it fix a memleak introduced > in Commit 08b3acd7a68f ("mm/memory_hotplug: Introduce offline_and_remove_memory()" > > Our test find a memleak in init_memory_block, it is clear that mem is never > been released due to wrong refcount. Commit 08b3acd7a68f ("mm/memory_hotplug: > Introduce offline_and_remove_memory()") failed to dec refcount after > find_memory_block which fail to dec refcount to zero in remove memory > causing the leak. > > Commit 8dc4bb58a146 ("mm/memory_hotplug: extend offline_and_remove_memory() > to handle more than one memory block") introduce walk_memory_blocks to > replace find_memory_block which dec refcount by calling put_device after > find_memory_block_by_id. In the way, the memleak is fixed. > > Here is the simplified calltrace: > > kmem_cache_alloc_trace+0x664/0xed0 > init_memory_block+0x8c/0x170 > create_memory_block_devices+0xa4/0x150 > add_memory_resource+0x188/0x530 > __add_memory+0x78/0x104 > add_memory+0x6c/0xb0 >
Makes sense to me. Of course, we could think about a simplified stable fix that only drops the ref.
-- Cheers,
David / dhildenb
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