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Subject: Re: [PATCH 02/19] mm/gup: factor out duplicate code from four
 routines
To:     Ira Weiny <ira.weiny@intel.com>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
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References: <20191030224930.3990755-1-jhubbard@nvidia.com>
 <20191030224930.3990755-3-jhubbard@nvidia.com>
 <20191031183549.GC14771@iweiny-DESK2.sc.intel.com>
From:   John Hubbard <jhubbard@nvidia.com>
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Date:   Thu, 31 Oct 2019 11:43:37 -0700
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On 10/31/19 11:35 AM, Ira Weiny wrote:
> On Wed, Oct 30, 2019 at 03:49:13PM -0700, John Hubbard wrote:
...
>> +
>> +static void __remove_refs_from_head(struct page *page, int refs)
>> +{
>> +	/* Do a get_page() first, in case refs == page->_refcount */
>> +	get_page(page);
>> +	page_ref_sub(page, refs);
>> +	put_page(page);
>> +}
> 
> I wonder if this is better implemented as "put_compound_head()"?  To match the
> try_get_compound_head() call below?

Hi Ira,

Good idea, I'll rename it to that.

> 
>> +
>> +static int __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr)
>> +{
>> +	*nr += nr_recorded_pages;
>> +	SetPageReferenced(head);
>> +	return 1;
> 
> When will this return anything but 1?
> 

Never, but it saves a line at all four call sites, by having it return like that.

I could see how maybe people would prefer to just have it be a void function,
and return 1 directly at the call sites. Since this was a lower line count I
thought maybe it would be slightly better, but it's hard to say really.

thanks,

John Hubbard
NVIDIA