On 3/17/2023 8:46 PM, Ryan Roberts wrote:
> On 17/03/2023 08:23, Yin, Fengwei wrote:
> [...]
>
>>>>>> FYI, I'm seeing a perf regression of about 1% when compiling the kernel on
>>>>>> Ampere Altra (arm64) with this whole series on top of v6.3-rc1 (In a VM using
>>>>>> ext4 filesystem). Looks like instruction aborts are taking much longer and a
>>>>>> selection of syscalls are a bit slower. Still hunting down the root cause. Will
>>>>>> report once I have conclusive diagnosis.
>>>>>
>>>>> I'm sorry - I'm struggling to find the exact cause. But its spending over 2x the
>>>>> amount of time in the instruction abort handling code once patches 32-36 are
>>>>> included. Everything in the flame graph is just taking longer. Perhaps we are
>>>>> getting more instruction aborts somehow? I have the flamegraphs if anyone wants
>>>>> them - just shout and I'll email them separately.
>>>> Thanks a lot to Ryan for sharing the flamegraphs to me. I found the __do_fault()
>>>> is called with patch 32-36 while no __do_fault() just with first 31 patches. I
>>>> suspect the folio_add_file_rmap_range() missed some PTEs population. Please give
>>>> me few days to find the root cause and fix. Sorry for this.
>>>
>>> You're welcome. Give me a shout once you have a re-spin and I'll rerun the tests.
>> Could you please help to try following changes? Thanks in advance.
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index 40be33b5ee46..137011320c68 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -3504,15 +3504,16 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>> if (!pte_none(vmf->pte[count]))
>> goto skip;
>>
>> - if (vmf->address == addr)
>> - ret = VM_FAULT_NOPAGE;
>> -
>> count++;
>> continue;
>> skip:
>> if (count) {
>> set_pte_range(vmf, folio, page, count, addr);
>> folio_ref_add(folio, count);
>> + if ((vmf->address < (addr + count * PAGE_SIZE)) &&
>> + (vmf->address >= addr))
>> + ret = VM_FAULT_NOPAGE;
>> +
>> }
>>
>> count++;
>> @@ -3525,6 +3526,9 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
>> if (count) {
>> set_pte_range(vmf, folio, page, count, addr);
>> folio_ref_add(folio, count);
>> + if ((vmf->address < (addr + count * PAGE_SIZE)) &&
>> + (vmf->address >= addr))
>> + ret = VM_FAULT_NOPAGE;
>> }
>>
>> vmf->pte = old_ptep;
>>
>
> I'm afraid this hasn't fixed it, and I still see __do_fault(). I'll send the
> flame graph over separately.
>
> Given I'm running on ext4, I wasn't expecting to see any large page cache
> folios? So I don't think we would have expected this patch to help anyway? (or
> perhaps there are still THP folios? But I think they will get PMD mapped?).
OK. I will try to reproduce the issue on my local env to see whether I could
reproduce it on x86_64 env.
Regards
Yin, Fengwei
>
>
>>
>> Regards
>> Yin, Fengwei
>>
>>>
>>>>
>>>>
>>>> Regards
>>>> Yin, Fengwei
>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Ryan
>>>>>>
>>>>>>
>>>>>>> + }
>>>>>>> +
>>>>>>> + if (first)
>>>>>>> + nr++;
>>>>>>> + } while (page++, --nr_pages > 0);
>>>>>>> } else if (folio_test_pmd_mappable(folio)) {
>>>>>>> /* That test is redundant: it's for safety or to optimize out */
>>>>>>>
>>>>>>> @@ -1354,6 +1362,30 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>>>>>> mlock_vma_folio(folio, vma, compound);
>>>>>>> }
>>>>>>>
>>>>>>> +/**
>>>>>>> + * page_add_file_rmap - add pte mapping to a file page
>>>>>>> + * @page: the page to add the mapping to
>>>>>>> + * @vma: the vm area in which the mapping is added
>>>>>>> + * @compound: charge the page as compound or small page
>>>>>>> + *
>>>>>>> + * The caller needs to hold the pte lock.
>>>>>>> + */
>>>>>>> +void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>>>>>> + bool compound)
>>>>>>> +{
>>>>>>> + struct folio *folio = page_folio(page);
>>>>>>> + unsigned int nr_pages;
>>>>>>> +
>>>>>>> + VM_WARN_ON_ONCE_PAGE(compound && !PageTransHuge(page), page);
>>>>>>> +
>>>>>>> + if (likely(!compound))
>>>>>>> + nr_pages = 1;
>>>>>>> + else
>>>>>>> + nr_pages = folio_nr_pages(folio);
>>>>>>> +
>>>>>>> + folio_add_file_rmap_range(folio, page, nr_pages, vma, compound);
>>>>>>> +}
>>>>>>> +
>>>>>>> /**
>>>>>>> * page_remove_rmap - take down pte mapping from a page
>>>>>>> * @page: page to remove mapping from
>>>>>>
>>>>>
>>>
>>>
>
