On 11/04/2024 16:00, David Hildenbrand wrote:
> On 11.04.24 16:54, Ryan Roberts wrote:
>> On 09/04/2024 09:26, Barry Song wrote:
>>> From: Barry Song <v-songbaohua@xxxxxxxx>
>>>
>>> Add a boolean argument named any_shared. If any of the swap entries are
>>> non-exclusive, set any_shared to true. The function do_swap_page() can
>>> then utilize this information to determine whether the entire large
>>> folio can be reused.
>>>
>>> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
>>> ---
>>> mm/internal.h | 9 ++++++++-
>>> mm/madvise.c | 2 +-
>>> mm/memory.c | 2 +-
>>> 3 files changed, 10 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/mm/internal.h b/mm/internal.h
>>> index 9d3250b4a08a..cae39c372bfc 100644
>>> --- a/mm/internal.h
>>> +++ b/mm/internal.h
>>> @@ -238,7 +238,8 @@ static inline pte_t pte_next_swp_offset(pte_t pte)
>>> *
>>> * Return: the number of table entries in the batch.
>>> */
>>> -static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, pte_t pte)
>>> +static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, pte_t pte,
>>> + bool *any_shared)
>>
>> Please update the docs in the comment above this for the new param; follow
>> folio_pte_batch()'s docs as a template.
>>
>>> {
>>> pte_t expected_pte = pte_next_swp_offset(pte);
>>> const pte_t *end_ptep = start_ptep + max_nr;
>>> @@ -248,12 +249,18 @@ static inline int swap_pte_batch(pte_t *start_ptep, int
>>> max_nr, pte_t pte)
>>> VM_WARN_ON(!is_swap_pte(pte));
>>> VM_WARN_ON(non_swap_entry(pte_to_swp_entry(pte)));
>>> + if (any_shared)
>>> + *any_shared |= !pte_swp_exclusive(pte);
>>
>> This is different from the approach in folio_pte_batch(). It inits *any_shared
>> to false and does NOT include the value of the first pte. I think that's odd,
>> personally and I prefer your approach. I'm not sure if there was a good reason
>> that David chose the other approach?
>
> Because in my case calling code does
>
> nr = folio_pte_batch(folio, addr, src_pte, pte, max_nr, flags,
> &any_writable);
>
> ...
>
> if (any_writable)
> pte = pte_mkwrite(pte, src_vma);
>
> ...
>
> and later checks in another function pte_write().
>
> So if the common pattern is that the original PTE will be used for checks, then
> it doesn't make sense to unnecessary checks+setting for the first PTE.
Yep understood. And I think adopting your semantics for any_shared actually
simplifies the code in patch 4 too; I've just commented that.
