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

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Message-ID: <38a2629d-689c-4592-9bd7-a77ab1b2045c@intel.com>
Date:   Mon, 2 Jul 2018 13:00:43 -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 07/02/2018 12:54 PM, Pavel Tatashin wrote:
> 
> 
> On 07/02/2018 03:47 PM, Dave Hansen wrote:
>> 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".
> 
> I called it pnum_end, because that is what is passed to
> sparse_init_nid(), but I see your point, and I can rename pnum_end to
> simply pnum if that will make things look better.

Could you just make it a helper that takes a beginning pnum and returns
the number of consecutive sections?

>> 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.
> 
> There is a comment before sparse_init_nid() about inclusiveness:
> 
> 434 /*
> 435  * Initialize sparse on a specific node. The node spans [pnum_begin, pnum_end)
> 436  * And number of present sections in this node is map_count.
> 437  */
> 438 static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
> 439                                    unsigned long pnum_end,
> 440                                    unsigned long map_count)

Which I totally missed.  Could you comment the code, please?