linux-kernel - Re: [PATCH v4 1/2] mm/memory_hotplug: split memmap_on

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Date:   Mon, 2 Oct 2023 11:28:44 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Vishal Verma <vishal.l.verma@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
        Huang Ying <ying.huang@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michal Hocko <mhocko@...e.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH v4 1/2] mm/memory_hotplug: split memmap_on_memory requests
 across memblocks


> +
> +static int __ref try_remove_memory(u64 start, u64 size)
> +{
> +	int rc, nid = NUMA_NO_NODE;
> +
> +	BUG_ON(check_hotplug_memory_range(start, size));
> +
> +	/*
> +	 * All memory blocks must be offlined before removing memory.  Check
> +	 * whether all memory blocks in question are offline and return error
> +	 * if this is not the case.
> +	 *
> +	 * While at it, determine the nid. Note that if we'd have mixed nodes,
> +	 * we'd only try to offline the last determined one -- which is good
> +	 * enough for the cases we care about.
> +	 */
> +	rc = walk_memory_blocks(start, size, &nid, check_memblock_offlined_cb);
> +	if (rc)
> +		return rc;
> +
> +	/*
> +	 * For memmap_on_memory, the altmaps could have been added on
> +	 * a per-memblock basis. Loop through the entire range if so,
> +	 * and remove each memblock and its altmap.
> +	 */
> +	if (mhp_memmap_on_memory()) {
> +		unsigned long memblock_size = memory_block_size_bytes();
> +		u64 cur_start;
> +
> +		for (cur_start = start; cur_start < start + size;
> +		     cur_start += memblock_size)
> +			__try_remove_memory(nid, cur_start, memblock_size);
> +	} else {
> +		__try_remove_memory(nid, start, size);
> +	}
> +
>   	return 0;
>   }

Why is the firmware, memblock and nid handling not kept in this outer 
function?

We really shouldn't be doing per memory block what needs to be done per 
memblock: remove_memory_block_devices() and arch_remove_memory().


-- 
Cheers,

David / dhildenb