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Re: [Xen-devel] [PATCH] xen/mm.h: add helper function to test-and-clear _PGC_allocated
- To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
- From: Jan Beulich <JBeulich@xxxxxxxx>
- Date: Mon, 15 Jul 2019 09:18:13 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, "Tim \(Xen.org\)" <tim@xxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxx>, JulienGrall <julien.grall@xxxxxxx>, Tamas K Lengyel <tamas@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, IanJackson <Ian.Jackson@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 15 Jul 2019 09:35:33 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHVNz5AbDzZgpaVWECo7hdqnCPqGqbEVHqAgAcOBACAAAtxAA==
- Thread-topic: [Xen-devel] [PATCH] xen/mm.h: add helper function to test-and-clear _PGC_allocated
On 15.07.2019 10:45, Paul Durrant wrote:
>> From: Jan Beulich <JBeulich@xxxxxxxx>
>> Sent: 10 July 2019 23:53
>>
>> On 10.07.2019 18:17, Paul Durrant wrote:
>>> @@ -418,13 +417,7 @@ static void hvm_free_ioreq_mfn(struct hvm_ioreq_server
>>> *s, bool buf)
>>> unmap_domain_page_global(iorp->va);
>>> iorp->va = NULL;
>>>
>>> - /*
>>> - * Check whether we need to clear the allocation reference before
>>> - * dropping the explicit references taken by get_page_and_type().
>>> - */
>>> - if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
>>> - put_page(page);
>>> -
>>> + clear_assignment_reference(page);
>>> put_page_and_type(page);
>>> }
>>
>> Is there a specific reason you drop the comment? It doesn't become
>> less relevant than when it was added, does it?
>
> Not sure, since what's actually going on is now internal to the function.
> If I change the function name to clear_allocation_reference() then I
> think the comment probably becomes extraneous.
Well, the perspective I'm taking is that the ordering constraint
wrt put_page_and_type() doesn't go away and is a relevant part of
what the comment talks about.
Jan
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