linux-kernel - Re: [RFC] atomic highmem kmap page pinning

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Date:	Fri, 6 Mar 2009 08:14:25 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Nicolas Pitre <nico@....org>, lkml <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org
Subject: Re: [RFC] atomic highmem kmap page pinning

On Fri, Mar 6, 2009 at 7:59 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Fri, Mar 06, 2009 at 07:23:44AM +0900, Minchan Kim wrote:
>> > +#ifdef ARCH_NEEDS_KMAP_HIGH_GET
>> > +/**
>> > + * kmap_high_get - pin a highmem page into memory
>> > + * @page: &struct page to pin
>> > + *
>> > + * Returns the page's current virtual memory address, or NULL if no mapping
>> > + * exists.  When and only when a non null address is returned then a
>> > + * matching call to kunmap_high() is necessary.
>> > + *
>> > + * This can be called from any context.
>> > + */
>> > +void *kmap_high_get(struct page *page)
>> > +{
>> > +       unsigned long vaddr, flags;
>> > +
>> > +       spin_lock_kmap_any(flags);
>> > +       vaddr = (unsigned long)page_address(page);
>> > +       if (vaddr) {
>> > +               BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
>> > +               pkmap_count[PKMAP_NR(vaddr)]++;
>> > +       }
>> > +       spin_unlock_kmap_any(flags);
>> > +       return (void*) vaddr;
>> > +}
>> > +#endif
>>
>> Let's add empty function for architecture of no ARCH_NEEDS_KMAP_HIGH_GET,
>
> The reasoning being?

I thought it can be used in common arm function.
so, for VIVT, it can be work but for VIPT, it can be nulled as
preventing compile error.

But, I don't know where we use kmap_high_get since I didn't see any
patch which use it.
If it is only used architecture specific place,  pz, forgot my comment.

-- 
Kinds regards,
Minchan Kim
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