On Mon, Jun 19, 2023 at 03:22:20PM +0800, 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
Ok, thanks for the information, now queued up.
greg k-h