Messages in this thread | | | Date | Wed, 27 Mar 2024 16:09:23 +0800 | Subject | Re: [PATCH 2/2] mm: support multi-size THP numa balancing | From | Baolin Wang <> |
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On 2024/3/27 10:04, Huang, Ying wrote: > Baolin Wang <baolin.wang@linux.alibaba.com> writes: > >> Now the anonymous page allocation already supports multi-size THP (mTHP), >> but the numa balancing still prohibits mTHP migration even though it is an >> exclusive mapping, which is unreasonable. >> >> Allow scanning mTHP: >> Commit 859d4adc3415 ("mm: numa: do not trap faults on shared data section >> pages") skips shared CoW pages' NUMA page migration to avoid shared data >> segment migration. In addition, commit 80d47f5de5e3 ("mm: don't try to >> NUMA-migrate COW pages that have other uses") change to use page_count() >> to avoid GUP pages migration, that will also skip the mTHP numa scaning. >> Theoretically, we can use folio_maybe_dma_pinned() to detect the GUP >> issue, although there is still a GUP race, the issue seems to have been >> resolved by commit 80d47f5de5e3. Meanwhile, use the folio_likely_mapped_shared() >> to skip shared CoW pages though this is not a precise sharers count. To >> check if the folio is shared, ideally we want to make sure every page is >> mapped to the same process, but doing that seems expensive and using >> the estimated mapcount seems can work when running autonuma benchmark. > > Because now we can deal with shared mTHP, it appears even possible to > remove folio_likely_mapped_shared() check?
IMO, the issue solved by commit 859d4adc3415 is about shared CoW mapping, and I prefer to measure it in another patch:)
>> Allow migrating mTHP: >> As mentioned in the previous thread[1], large folios (including THP) are >> more susceptible to false sharing issues among threads than 4K base page, >> leading to pages ping-pong back and forth during numa balancing, which is >> currently not easy to resolve. Therefore, as a start to support mTHP numa >> balancing, we can follow the PMD mapped THP's strategy, that means we can >> reuse the 2-stage filter in should_numa_migrate_memory() to check if the >> mTHP is being heavily contended among threads (through checking the CPU id >> and pid of the last access) to avoid false sharing at some degree. Thus, >> we can restore all PTE maps upon the first hint page fault of a large folio >> to follow the PMD mapped THP's strategy. In the future, we can continue to >> optimize the NUMA balancing algorithm to avoid the false sharing issue with >> large folios as much as possible. >> >> Performance data: >> Machine environment: 2 nodes, 128 cores Intel(R) Xeon(R) Platinum >> Base: 2024-03-25 mm-unstable branch >> Enable mTHP to run autonuma-benchmark >> >> mTHP:16K >> Base Patched >> numa01 numa01 >> 224.70 137.23 >> numa01_THREAD_ALLOC numa01_THREAD_ALLOC >> 118.05 50.57 >> numa02 numa02 >> 13.45 9.30 >> numa02_SMT numa02_SMT >> 14.80 7.43 >> >> mTHP:64K >> Base Patched >> numa01 numa01 >> 216.15 135.20 >> numa01_THREAD_ALLOC numa01_THREAD_ALLOC >> 115.35 46.93 >> numa02 numa02 >> 13.24 9.24 >> numa02_SMT numa02_SMT >> 14.67 7.31 >> >> mTHP:128K >> Base Patched >> numa01 numa01 >> 205.13 140.41 >> numa01_THREAD_ALLOC numa01_THREAD_ALLOC >> 112.93 44.78 >> numa02 numa02 >> 13.16 9.19 >> numa02_SMT numa02_SMT >> 14.81 7.39 >> >> [1] https://lore.kernel.org/all/20231117100745.fnpijbk4xgmals3k@techsingularity.net/ >> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> >> --- >> mm/memory.c | 56 +++++++++++++++++++++++++++++++++++++++++++-------- >> mm/mprotect.c | 3 ++- >> 2 files changed, 50 insertions(+), 9 deletions(-) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index c30fb4b95e15..36191a9c799c 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -5068,16 +5068,55 @@ static void numa_rebuild_single_mapping(struct vm_fault *vmf, struct vm_area_str >> update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1); >> } >> >> +static void numa_rebuild_large_mapping(struct vm_fault *vmf, struct vm_area_struct *vma, >> + struct folio *folio, pte_t fault_pte, bool ignore_writable) >> +{ >> + int nr = pte_pfn(fault_pte) - folio_pfn(folio); >> + unsigned long start = max(vmf->address - nr * PAGE_SIZE, vma->vm_start); >> + unsigned long end = min(start + folio_nr_pages(folio) * PAGE_SIZE, vma->vm_end); > > If start is in the middle of folio, it's possible for end to go beyond > the end of folio. So, should be something like below?
Yes, good catch, even though below iteration can skip over the parts that exceed the size of that folio.
> unsigned long end = min(vmf->address + (folio_nr_pages(folio) - nr) * PAGE_SIZE, vma->vm_end);
Yes, this looks good to me. Will do in next version. Thanks.
>> + pte_t *start_ptep = vmf->pte - (vmf->address - start) / PAGE_SIZE; >> + bool pte_write_upgrade = vma_wants_manual_pte_write_upgrade(vma); >> + unsigned long addr; >> + >> + /* Restore all PTEs' mapping of the large folio */ >> + for (addr = start; addr != end; start_ptep++, addr += PAGE_SIZE) { >> + pte_t pte, old_pte; >> + pte_t ptent = ptep_get(start_ptep); >> + bool writable = false; >> + >> + if (!pte_present(ptent) || !pte_protnone(ptent)) >> + continue; >> + >> + if (vm_normal_folio(vma, addr, ptent) != folio) >> + continue; >> + >> + if (!ignore_writable) { >> + writable = pte_write(pte); >> + if (!writable && pte_write_upgrade && >> + can_change_pte_writable(vma, addr, pte)) >> + writable = true; >> + } >> + >> + old_pte = ptep_modify_prot_start(vma, addr, start_ptep); >> + pte = pte_modify(old_pte, vma->vm_page_prot); >> + pte = pte_mkyoung(pte); >> + if (writable) >> + pte = pte_mkwrite(pte, vma); >> + ptep_modify_prot_commit(vma, addr, start_ptep, old_pte, pte); >> + update_mmu_cache_range(vmf, vma, addr, start_ptep, 1); > > Can this be batched for the whole folio?
I thought about it, but things are a little tricky. The folio may not contain continuous protnone PTEs, should skip non-present or non-protnone PTEs.
Moreover, it is necessary to define architecture-specified ptep_modify_prot_start*_nr and ptep_modify_prot_commit*_nr that can handle multiple PTEs, which is in my TODO list including batch numa scanning in change_pte_range().
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