linux-kernel - Re: [PATCH 04/11] ARCv2: mm: THP support

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Message-ID: <55DF414C.6070601@synopsys.com>
Date:	Thu, 27 Aug 2015 22:26:44 +0530
From:	Vineet Gupta <vgupta@...opsys.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Minchan Kim <minchan@...nel.org>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	arc-linux-dev@...opsys.com
Subject: Re: [PATCH 04/11] ARCv2: mm: THP support

On Thursday 27 August 2015 09:02 PM, Kirill A. Shutemov wrote:
> On Thu, Aug 27, 2015 at 02:33:07PM +0530, Vineet Gupta wrote:
>> > +pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
>> > +{
>> > +	struct list_head *lh;
>> > +	pgtable_t pgtable;
>> > +	pte_t *ptep;
>> > +
>> > +	assert_spin_locked(&mm->page_table_lock);
>> > +
>> > +	pgtable = pmd_huge_pte(mm, pmdp);
>> > +	lh = (struct list_head *) pgtable;
>> > +	if (list_empty(lh))
>> > +		pmd_huge_pte(mm, pmdp) = (pgtable_t) NULL;
>> > +	else {
>> > +		pmd_huge_pte(mm, pmdp) = (pgtable_t) lh->next;
>> > +		list_del(lh);
>> > +	}
> Side question: why pgtable_t is unsigned long on ARC and not struct page *
> or pte_t *, like on other archs? We could avoid these casts.

This goes back how I did this for ARC long back to avoid page_address() calls in
general case. e.g. pte_alloc_one(), pmd_populate(), pte_free()... all needed to
convert struct page to unsigned long. It was micro-optimization of sorts, but
served us well.

I could perhaps see try making it pte *, that will certainly remove a bunch of
other casts as well.

-Vineet


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