linux-kernel - Re: [PATCH v4 1/4] driver/base: Optimize memory block registration to reduce boot time

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Message-ID: <a3072d7f-235e-4224-9867-4cebb66ca4fb@redhat.com>
Date: Fri, 16 May 2025 12:12:26 +0200
From: David Hildenbrand <david@...hat.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Donet Tom <donettom@...ux.ibm.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Oscar Salvador
 <osalvador@...e.de>, Zi Yan <ziy@...dia.com>,
 Ritesh Harjani <ritesh.list@...il.com>, rafael@...nel.org,
 Danilo Krummrich <dakr@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Yury Norov <yury.norov@...il.com>, Dave Jiang <dave.jiang@...el.com>
Subject: Re: [PATCH v4 1/4] driver/base: Optimize memory block registration to
 reduce boot time

>> We'd have to be smart about memory blocks that fall into multiple regions,
>> but it should be a corner case and doable.
> 
> This is a corner case that should be handled regardless of the loop order.
> And I don't think it's handled today at all.
> 
> If we have a block that crosses node boundaries, current implementation of
> register_mem_block_under_node_early() will register it under the first
> node.

At least upstream behavior should be that it would be linked under all 
nodes. At least that's what I remember :)

>   
>> OTOH, we usually don't expect having a lot of regions, so iterating over
>> them is probably not a big bottleneck? Anyhow, just wanted to raise it.
> 
> There would be at least a region per node and having
> 
> for_each_online_node()
> 	for_each_mem_region()
> 
> makes the loop O(n²) for no good reason.

Yes, that's why I mentioned it. If we have many nodes it might 
definitely be relevant.

-- 
Cheers,

David / dhildenb