Messages in this thread | | | Date | Thu, 28 Mar 2024 19:34:34 +0800 | Subject | Re: [PATCH 2/2] mm: support multi-size THP numa balancing | From | Baolin Wang <> |
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On 2024/3/28 17:25, David Hildenbrand wrote: > On 26.03.24 12:51, Baolin Wang wrote: >> 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. >> >> 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); >> + 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; >> + > > Should you be using folio_pte_batch() in the caller to collect all > applicable PTEs and then only have function that batch-changes a given > nr of PTEs? > > (just like we are now batching other stuff)
Seems folio_pte_batch() is not suitable for numa balancing, since we did not care about other PTE bits, only care about the protnone bits. And after more thinking, I think I can drop the vm_normal_folio() validation, since all PTEs are ensured to be within the range of the folio size.
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