Re: [PATCH v2 1/3] hugetlb: Convert hugetlb_fault() to use struct vm_fault

Muchun Song
2024-04-07T07:37:19Z

> On Apr 5, 2024, at 03:32, Vishal Moola <vishal.moola@gmail.com> wrote:
>
> On Thu, Apr 4, 2024 at 5:26 AM Oscar Salvador <osalvador@suse.de> wrote:
>>
>> On Mon, Apr 01, 2024 at 01:26:49PM -0700, Vishal Moola (Oracle) wrote:
>>> Now that hugetlb_fault() has a vm_fault available for fault tracking, use
>>> it throughout. This cleans up the code by removing 2 variables, and
>>> prepares hugetlb_fault() to take in a struct vm_fault argument.
>>>
>>> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
>>
>> Reviewed-by: Oscar Salvador <osalvador@suse.de>
>>
>> A question below:
>>
>>> mm/hugetlb.c | 84 +++++++++++++++++++++++++---------------------------
>>> 1 file changed, 41 insertions(+), 43 deletions(-)
>>>
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 8267e221ca5d..360b82374a89 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>> ...
>>> /*
>>> - * entry could be a migration/hwpoison entry at this point, so this
>>> - * check prevents the kernel from going below assuming that we have
>>> - * an active hugepage in pagecache. This goto expects the 2nd page
>>> - * fault, and is_hugetlb_entry_(migration|hwpoisoned) check will
>>> - * properly handle it.
>>> + * vmf.orig_pte could be a migration/hwpoison vmf.orig_pte at this
>>
>> "vmf.orig_pte could be a migration/hwpoison entry at ..."
>>
>>> - entry = pte_mkyoung(entry);
>>> - if (huge_ptep_set_access_flags(vma, haddr, ptep, entry,
>>> + vmf.orig_pte = pte_mkyoung(vmf.orig_pte);
>>> + if (huge_ptep_set_access_flags(vma, vmf.address, vmf.pte, vmf.orig_pte,
>>> flags & FAULT_FLAG_WRITE))
>>
>> Would it make sense to teach huge_ptep_set_access_flags/set_huge_pte_at() to use
>> vm_fault struct as well? All info we are passing is stored there.
>> Maybe it is not worth the trouble though, just asking.
>
> Yeah, it makes sense. There are actually many function calls in the
> hugetlb_fault() and
> __handle_mm_fault() pathways that could make use of vm_fault to clean
> up the stack.
>
> It's not particularly complicated either, aside from reorganizing some
> variables for every
> implementation of each function. I'm not really sure if it's worth
> dedicated effort
> and churn though (at least I'm not focused on that for now).

Not all the users of set_huge_pte_at() have a vmf structure. So I do not
think it is a good idea to change it. And huge_ptep_set_access_flags() is
a variant of ptep_set_access_flags(), it's better to keep consistent.
Otherwise, I think both of them should be adapted if you want cleanup.
My tendency is to remain unchanged.

Muchun,
Thanks.