linux-kernel - Re: [PATCH RFC 1/1] numa: fix /proc/<pid>/numa

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Message-ID: <20160205170317.4906cba3@thinkpad>
Date:	Fri, 5 Feb 2016 17:03:17 +0100
From:	Gerald Schaefer <gerald.schaefer@...ibm.com>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Michal Hocko <mhocko@...e.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	Dan Williams <dan.j.williams@...el.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC 1/1] numa: fix /proc/<pid>/numa_maps for THP

On Fri, 5 Feb 2016 07:38:09 -0800
Dave Hansen <dave.hansen@...el.com> wrote:

> On 02/05/2016 07:34 AM, Gerald Schaefer wrote:
> > +static struct page *can_gather_numa_stats_pmd(pmd_t pmd,
> > +					      struct vm_area_struct *vma,
> > +					      unsigned long addr)
> > +{
> 
> Is there a way to do this without making a copy of most of
> can_gather_numa_stats()?  Seems like the kind of thing where the pmd
> version will bitrot.
> 

Yes, that also gave me a little headache, even more with the vm_normal_page()
code duplication, but I didn't see a much better way. Separate _pte/_pmd
functions that largely do the same thing seem not so uncommon to me.

The best I could think of would be splitting the !HAVE_PTE_SPECIAL path
in vm_normal_page() into a separate function, but I see not much room for
improvement for can_gather_numa_stats(), other than maybe not having
a _pmd version at all and doing all the work inside gather_pte_stats(),
but that would probably just relocate the code duplication.