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SubjectRe: [PATCH v3 09/11] mm/memory_hotplug: Remove memory block devices before arch_remove_memory()
On 01.07.19 10:41, Michal Hocko wrote:
> On Mon 27-05-19 13:11:50, David Hildenbrand wrote:
>> Let's factor out removing of memory block devices, which is only
>> necessary for memory added via add_memory() and friends that created
>> memory block devices. Remove the devices before calling
>> arch_remove_memory().
>> This finishes factoring out memory block device handling from
>> arch_add_memory() and arch_remove_memory().
> OK, this makes sense again. Just a nit. Calling find_memory_block_by_id
> for each memory block looks a bit suboptimal, especially when we are
> removing consequent physical memblocks. I have to confess that I do not
> know how expensive is the search and I also expect that there won't be
> that many memblocks in the removed range anyway as large setups have
> large memblocks.

The devices are not allocated sequentially, so there is no easy way to
look them up.

There is a comment for find_memory_block():

"For now, we have a linear search to go find the appropriate
memory_block corresponding to a particular phys_index. If this gets to
be a real problem, we can always use a radix tree or something here."

So if this becomes a problem, we need a separate data structure to speed
up the lookup. (IOW, this was already the same in the old code)




David / dhildenb

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