linux-kernel - Re: [PATCH v11 04/25] mm: devmap: refactor 1-based refcounting for ZONE

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Date:   Wed, 18 Dec 2019 23:33:36 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
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        Christoph Hellwig <hch@...radead.org>,
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        Dave Chinner <david@...morbit.com>,
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Subject: Re: [PATCH v11 04/25] mm: devmap: refactor 1-based refcounting for
 ZONE_DEVICE pages

On 12/18/19 10:52 PM, Dan Williams wrote:
> On Wed, Dec 18, 2019 at 9:51 PM John Hubbard <jhubbard@...dia.com> wrote:
>>
>> On 12/18/19 9:27 PM, Dan Williams wrote:
>> ...
>>>> @@ -461,5 +449,5 @@ void __put_devmap_managed_page(struct page *page)
>>>>           page->mapping = NULL;
>>>>           page->pgmap->ops->page_free(page);
>>>>    }
>>>> -EXPORT_SYMBOL(__put_devmap_managed_page);
>>>> +EXPORT_SYMBOL(free_devmap_managed_page);
>>>
>>> This patch does not have a module consumer for
>>> free_devmap_managed_page(), so the export should move to the patch
>>> that needs the new export.
>>
>> Hi Dan,
>>
>> OK, I know that's a policy--although it seems quite pointless here given
>> that this is definitely going to need an EXPORT.
>>
>> At the moment, the series doesn't use it in any module at all, so I'll just
>> delete the EXPORT for now.
>>
>>>
>>> Also the only reason that put_devmap_managed_page() is EXPORT_SYMBOL
>>> instead of EXPORT_SYMBOL_GPL is that there was no practical way to
>>> hide the devmap details from evey module in the kernel that did
>>> put_page(). I would expect free_devmap_managed_page() to
>>> EXPORT_SYMBOL_GPL if it is not inlined into an existing exported
>>> static inline api.
>>>
>>
>> Sure, I'll change it to EXPORT_SYMBOL_GPL when the time comes. We do have
>> to be careful that we don't shut out normal put_page() types of callers,
>> but...glancing through the current callers, that doesn't look to be a problem.
>> Good. So it should be OK to do EXPORT_SYMBOL_GPL here.
>>
>> Are you *sure* you don't want to just pre-emptively EXPORT now, and save
>> looking at it again?
> 
> I'm positive. There is enough history for "trust me the consumer is
> coming" turning out not to be true to justify the hassle in my mind. I
> do trust you, but things happen.
> 

OK, it's deleted locally. Thanks for looking at the patch. I'll post a v12 series
that includes the change, once it looks like reviews are slowing down.


thanks,
-- 
John Hubbard
NVIDIA