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SubjectRe: [PATCH] drivers/base/memory.c: memory subsys init: skip search for missing blocks
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On 01.11.19 19:10, Scott Cheloha wrote:
> Add a flag to init_memory_block() to enable/disable searching for a
> matching block before creating a device for the block and adding it to
> the memory subsystem's bus.
>
> When the memory subsystem is being initialized there is no need to check
> if a given block has already been added to its bus. The bus is new, so the
> block in question cannot yet have a corresponding device.
>
> The search for a missing block is O(n) so this saves substantial time at
> boot if there are many such blocks to add.
>
> Signed-off-by: Scott Cheloha <cheloha@linux.vnet.ibm.com>
> ---
> drivers/base/memory.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 55907c27075b..1160df4a8feb 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -643,17 +643,21 @@ int register_memory(struct memory_block *memory)
> }
>
> static int init_memory_block(struct memory_block **memory,
> - unsigned long block_id, unsigned long state)
> + unsigned long block_id, unsigned long state,
> + bool may_exist)
> {
> struct memory_block *mem;
> unsigned long start_pfn;
> int ret = 0;
>
> - mem = find_memory_block_by_id(block_id);
> - if (mem) {
> - put_device(&mem->dev);
> - return -EEXIST;
> + if (may_exist) {
> + mem = find_memory_block_by_id(block_id);
> + if (mem) {
> + put_device(&mem->dev);
> + return -EEXIST;
> + }

No, I don't really like that. Can we please speed up the lookup via a
radix tree as noted in the comment of "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.
*
* This could be made generic for all device subsystems.
*/

This will speed up all users of walk_memory_blocks() similarly.
Especially, it will also speed up link_mem_sections() used during boot,
which relies on walk_memory_blocks().

--

Thanks,

David / dhildenb

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