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Message-ID: <160264d0-8110-bda3-eb77-381ac9482dd6@redhat.com>
Date:   Tue, 6 Jun 2023 09:46:36 +0200
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Subject: Re: [PATCH v3] mm/migrate_device: Try to handle swapcache pages
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From:   David Hildenbrand <david@redhat.com>
To:     mpenttil@redhat.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Cc:     Alistair Popple <apopple@nvidia.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        "Huang, Ying" <ying.huang@intel.com>
References: <20230606050149.25699-1-mpenttil@redhat.com>
 <5a3a4025-9dff-713b-8891-fef2bd450b01@redhat.com>
Organization: Red Hat
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On 06.06.23 09:44, David Hildenbrand wrote:
> On 06.06.23 07:01, mpenttil@redhat.com wrote:
>> From: Mika Penttilä <mpenttil@redhat.com>
>>
>> Migrating file pages and swapcache pages into device memory is not supported.
>> The decision is done based on page_mapping(). For now, swapcache pages are not migrated.
>>
>> Things can however be improved, for swapcache pages. Try to get rid of the swap cache,
>> and if successful, go ahead as with other anonymous pages.
>>
>> Cc: Alistair Popple <apopple@nvidia.com>
>> Cc: John Hubbard <jhubbard@nvidia.com>
>> Cc: Ralph Campbell <rcampbell@nvidia.com>
>> Cc: "Huang, Ying" <ying.huang@intel.com>
>> Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
>> Reviewed-by: Alistair Popple <apopple@nvidia.com>
>> Signed-off-by: Mika Penttilä <mpenttil@redhat.com>
>> ---
>>
>> v3:
>>     - Adjust comments
>>     - Add Reviewed-bys
>>
>> v2:
>>     - use folio_test_anon() (Huang, Ying)
>>
>>    mm/migrate_device.c | 22 ++++++++++++++++------
>>    1 file changed, 16 insertions(+), 6 deletions(-)
>>
>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
>> index d30c9de60b0d..f76ebccfe067 100644
>> --- a/mm/migrate_device.c
>> +++ b/mm/migrate_device.c
>> @@ -747,13 +747,23 @@ static void __migrate_device_pages(unsigned long *src_pfns,
>>    
>>    		if (is_device_private_page(newpage) ||
>>    		    is_device_coherent_page(newpage)) {
>> -			/*
>> -			 * For now only support anonymous memory migrating to
>> -			 * device private or coherent memory.
>> -			 */
>> +
>>    			if (mapping) {
>> -				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
>> -				continue;
>> +				struct folio *folio;
>> +
>> +				folio = page_folio(page);
>> +
>> +				/*
>> +				 * For now only support anonymous memory migrating to
>> +				 * device private or coherent memory.
>> +				 *
>> +				 * Try to get rid of swap cache if possible.
>> +				 *
>> +				 */
>> +				if (!folio_test_anon(folio) || !folio_free_swap(folio)) {
>> +					src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
>> +					continue;
> 
> I'm pretty sure the folio has to be locked in order to call
> folio_free_swap().
> 

Oh, staring at the bigger context, I assume we locked the folios via 
migrate_device_range(), correct?

-- 
Cheers,

David / dhildenb