linux-kernel - Re: [PATCH v3 2/2] mm/sparse: start using sparse_init

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Date:   Mon, 2 Jul 2018 12:47:29 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        linux-mm@...ck.org, dan.j.williams@...el.com, jack@...e.cz,
        jglisse@...hat.com, jrdr.linux@...il.com, bhe@...hat.com,
        gregkh@...uxfoundation.org, vbabka@...e.cz,
        richard.weiyang@...il.com, rientjes@...gle.com, mingo@...nel.org,
        osalvador@...hadventures.net
Subject: Re: [PATCH v3 2/2] mm/sparse: start using sparse_init_nid(), and
 remove old code

On 07/01/2018 07:04 PM, Pavel Tatashin wrote:
> +	for_each_present_section_nr(pnum_begin + 1, pnum_end) {
> +		int nid = sparse_early_nid(__nr_to_section(pnum_end));
>  
> +		if (nid == nid_begin) {
> +			map_count++;
>  			continue;
>  		}

> +		sparse_init_nid(nid_begin, pnum_begin, pnum_end, map_count);
> +		nid_begin = nid;
> +		pnum_begin = pnum_end;
> +		map_count = 1;
>  	}

Ugh, this is really hard to read.  Especially because the pnum "counter"
is called "pnum_end".

So, this is basically a loop that collects all of the adjacent sections
in a given single nid and then calls sparse_init_nid().  pnum_end in
this case is non-inclusive, so the sparse_init_nid() call is actually
for the *previous* nid that pnum_end is pointing _past_.

This *really* needs commenting.