> On Sep 19, 2023, at 16:55, Joao Martins <joao.m.martins@xxxxxxxxxx> wrote:
>
> On 19/09/2023 09:41, Muchun Song wrote:
>>> On Sep 19, 2023, at 16:26, Joao Martins <joao.m.martins@xxxxxxxxxx> wrote:
>>> On 19/09/2023 07:42, Muchun Song wrote:
>>>> On 2023/9/19 07:01, Mike Kravetz wrote:
>>>>> From: Joao Martins <joao.m.martins@xxxxxxxxxx>
>>>>>
>>>>> In an effort to minimize amount of TLB flushes, batch all PMD splits
>>>>> belonging to a range of pages in order to perform only 1 (global) TLB
>>>>> flush.
>>>>>
>>>>> Add a flags field to the walker and pass whether it's a bulk allocation
>>>>> or just a single page to decide to remap. First value
>>>>> (VMEMMAP_SPLIT_NO_TLB_FLUSH) designates the request to not do the TLB
>>>>> flush when we split the PMD.
>>>>>
>>>>> Rebased and updated by Mike Kravetz
>>>>>
>>>>> Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
>>>>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>>>>> ---
>>>>> mm/hugetlb_vmemmap.c | 79 +++++++++++++++++++++++++++++++++++++++++---
>>>>> 1 file changed, 75 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
>>>>> index 147ed15bcae4..e8bc2f7567db 100644
>>>>> --- a/mm/hugetlb_vmemmap.c
>>>>> +++ b/mm/hugetlb_vmemmap.c
>>>>> @@ -27,6 +27,7 @@
>>>>> * @reuse_addr: the virtual address of the @reuse_page page.
>>>>> * @vmemmap_pages: the list head of the vmemmap pages that can be freed
>>>>> * or is mapped from.
>>>>> + * @flags: used to modify behavior in bulk operations
>>>>
>>>> Better to describe it as "used to modify behavior in vmemmap page table walking
>>>> operations"
>>>>
>>> OK
>>>
>>>>> void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head
>>>>> *folio_list)
>>>>> {
>>>>> struct folio *folio;
>>>>> LIST_HEAD(vmemmap_pages);
>>>>> + list_for_each_entry(folio, folio_list, lru)
>>>>> + hugetlb_vmemmap_split(h, &folio->page);
>>>>> +
>>>>> + flush_tlb_all();
>>>>> +
>>>>> list_for_each_entry(folio, folio_list, lru) {
>>>>> int ret = __hugetlb_vmemmap_optimize(h, &folio->page,
>>>>> &vmemmap_pages);
>>>>
>>>> This is unlikely to be failed since the page table allocation
>>>> is moved to the above
>>>
>>>> (Note that the head vmemmap page allocation
>>>> is not mandatory).
>>>
>>> Good point that I almost forgot
>>>
>>>> So we should handle the error case in the above
>>>> splitting operation.
>>>
>>> But back to the previous discussion in v2... the thinking was that /some/ PMDs
>>> got split, and say could allow some PTE remapping to occur and free some pages
>>> back (each page allows 6 more splits worst case). Then the next
>>> __hugetlb_vmemmap_optimize() will have to split PMD pages again for those
>>> hugepages that failed the batch PMD split (as we only defer the PTE remap tlb
>>> flush in this stage).
>>
>> Oh, yes. Maybe we could break the above traversal as early as possible
>> once we enter an ENOMEM?
>>
>
> Sounds good -- no point in keep trying to split if we are failing with OOM.
>
> Perhaps a comment in both of these clauses (the early break on split and the OOM
> handling in batch optimize) could help make this clear.
Make sense.
Thanks.
>
>>>
>>> Unless this isn't something worth handling
>>>
>>> Joao
