linux-kernel - Re: [PATCH v8 09/12] mm/sparsemem: Support sub-section hotplug

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Date:   Thu, 09 May 2019 01:15:32 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Dan Williams <dan.j.williams@...el.com>, akpm@...ux-foundation.org
Cc:     Michal Hocko <mhocko@...e.com>, Vlastimil Babka <vbabka@...e.cz>,
        Logan Gunthorpe <logang@...tatee.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 09/12] mm/sparsemem: Support sub-section hotplug

On Mon, 2019-05-06 at 16:40 -0700, Dan Williams wrote:
> @@ -741,49 +895,31 @@ int __meminit sparse_add_section(int nid,
> unsigned long start_pfn,
>  		unsigned long nr_pages, struct vmem_altmap *altmap)
>  {
>  	unsigned long section_nr = pfn_to_section_nr(start_pfn);
> -	struct mem_section_usage *usage;
>  	struct mem_section *ms;
>  	struct page *memmap;
>  	int ret;

I already pointed this out in v7, but:

>  
> -	/*
> -	 * no locking for this, because it does its own
> -	 * plus, it does a kmalloc
> -	 */
>  	ret = sparse_index_init(section_nr, nid);
>  	if (ret < 0 && ret != -EEXIST)
>  		return ret;

sparse_index_init() only returns either -ENOMEM or 0, so the above can
be:

	if (ret < 0) or if (ret)

> -	ret = 0;
> -	memmap = populate_section_memmap(start_pfn,
> PAGES_PER_SECTION, nid,
> -			altmap);
> -	if (!memmap)
> -		return -ENOMEM;
> -	usage = kzalloc(mem_section_usage_size(), GFP_KERNEL);
> -	if (!usage) {
> -		depopulate_section_memmap(start_pfn,
> PAGES_PER_SECTION, altmap);
> -		return -ENOMEM;
> -	}
>  
> -	ms = __pfn_to_section(start_pfn);
> -	if (ms->section_mem_map & SECTION_MARKED_PRESENT) {
> -		ret = -EEXIST;
> -		goto out;
> -	}
> +	memmap = section_activate(nid, start_pfn, nr_pages, altmap);
> +	if (IS_ERR(memmap))
> +		return PTR_ERR(memmap);
> +	ret = 0;

If we got here, sparse_index_init must have returned 0, so ret already
contains 0.
We can remove the assignment.

>  
>  	/*
>  	 * Poison uninitialized struct pages in order to catch
> invalid flags
>  	 * combinations.
>  	 */
> -	page_init_poison(memmap, sizeof(struct page) *
> PAGES_PER_SECTION);
> +	page_init_poison(pfn_to_page(start_pfn), sizeof(struct page)
> * nr_pages);
>  
> +	ms = __pfn_to_section(start_pfn);
>  	section_mark_present(ms);
> -	sparse_init_one_section(ms, section_nr, memmap, usage);
> +	sparse_init_one_section(ms, section_nr, memmap, ms->usage);
>  
> -out:
> -	if (ret < 0) {
> -		kfree(usage);
> -		depopulate_section_memmap(start_pfn,
> PAGES_PER_SECTION, altmap);
> -	}
> +	if (ret < 0)
> +		section_deactivate(start_pfn, nr_pages, nid,
> altmap);

AFAICS, ret is only set by the return code from sparse_index_init, so
we cannot really get to this code being ret different than 0.
So we can remove the above two lines.

I will start reviewing the patches that lack review from this version
soon.

-- 
Oscar Salvador
SUSE L3