Mika Penttilä <mpenttil@xxxxxxxxxx> writes:
> H,
>
>
> On 8.5.2023 5.26, Huang, Ying wrote:
>> mpenttil@xxxxxxxxxx writes:
>>
>>> From: Mika Penttil <mpenttil@xxxxxxxxxx>
>>>
>>> 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.
>>>
>>> As a detail, do not mess with shmem pages, as they handle swap internally.
>>>
>>> Cc: Alistair Popple <apopple@xxxxxxxxxx>
>>> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
>>> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
>>> Signed-off-by: Mika Penttil <mpenttil@xxxxxxxxxx>
>>> ---
>>> mm/migrate_device.c | 12 ++++++++++--
>>> 1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
>>> index d30c9de60b0d..e8169c58c341 100644
>>> --- a/mm/migrate_device.c
>>> +++ b/mm/migrate_device.c
>>> @@ -12,6 +12,7 @@
>>> #include <linux/mmu_notifier.h>
>>> #include <linux/oom.h>
>>> #include <linux/pagewalk.h>
>>> +#include <linux/shmem_fs.h>
>>> #include <linux/rmap.h>
>>> #include <linux/swapops.h>
>>> #include <asm/tlbflush.h>
>>> @@ -750,10 +751,17 @@ static void __migrate_device_pages(unsigned long *src_pfns,
>>> /*
>>> * For now only support anonymous memory migrating to
>>> * device private or coherent memory.
>>> + *
>>> + * Try to get rid of swap cache if possible.
>>> + * Leave shmem pages alone, they handle swap internally
>>> + *
>>> */
>>> if (mapping) {
>>> - src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
>>> - continue;
>>> + if (shmem_mapping(mapping) ||
>>> + !folio_free_swap(page_folio(page))) {
>> Should we filter out file pages firstly?
>
> folio_free_swap() checks first and returns false if not swapcache page
> (ie including normal file pages) so think that is enough,
You are right. folio_free_swap() will call folio_test_swapcache(), and
which will check folio_test_swapbacked().
And, IIUC, we don't need to check shmem too. Because folio_free_swap()
will not return true for shmem pages.
> but maybe for clarity and not depending on it, could be good
> explicitly check for swapcache before calling folio_free_swap().
Yes. That will be more clear. I suggest to use folio_test_anon(), that
will filter out shmem pages too.
>>
>>> + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
>>> + continue;
>>> + }
>>> }
>>> } else if (is_zone_device_page(newpage)) {
>>> /*
Best Regards,
Huang, Ying
