6.6-stable review patch. If anyone has any objections, please let me know.
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From: Zi Yan ziy@nvidia.com
commit fd8c35a92910f4829b7c99841f39b1b952c259d5 upstream.
When handling a numa page fault, task_numa_fault() should be called by a process that restores the page table of the faulted folio to avoid duplicated stats counting. Commit c5b5a3dd2c1f ("mm: thp: refactor NUMA fault handling") restructured do_huge_pmd_numa_page() and did not avoid task_numa_fault() call in the second page table check after a numa migration failure. Fix it by making all !pmd_same() return immediately.
This issue can cause task_numa_fault() being called more than necessary and lead to unexpected numa balancing results (It is hard to tell whether the issue will cause positive or negative performance impact due to duplicated numa fault counting).
Link: https://lkml.kernel.org/r/20240809145906.1513458-3-ziy@nvidia.com Fixes: c5b5a3dd2c1f ("mm: thp: refactor NUMA fault handling") Reported-by: "Huang, Ying" ying.huang@intel.com Closes: https://lore.kernel.org/linux-mm/87zfqfw0yw.fsf@yhuang6-desk2.ccr.corp.intel... Signed-off-by: Zi Yan ziy@nvidia.com Acked-by: David Hildenbrand david@redhat.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: "Huang, Ying" ying.huang@intel.com Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: Mel Gorman mgorman@suse.de Cc: Yang Shi shy828301@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/huge_memory.c | 30 +++++++++++++----------------- 1 file changed, 13 insertions(+), 17 deletions(-)
--- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1504,7 +1504,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) { spin_unlock(vmf->ptl); - goto out; + return 0; }
pmd = pmd_modify(oldpmd, vma->vm_page_prot); @@ -1548,23 +1548,16 @@ vm_fault_t do_huge_pmd_numa_page(struct if (migrated) { flags |= TNF_MIGRATED; page_nid = target_nid; - } else { - flags |= TNF_MIGRATE_FAIL; - vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); - if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) { - spin_unlock(vmf->ptl); - goto out; - } - goto out_map; + task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags); + return 0; }
-out: - if (page_nid != NUMA_NO_NODE) - task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, - flags); - - return 0; - + flags |= TNF_MIGRATE_FAIL; + vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); + if (unlikely(!pmd_same(oldpmd, *vmf->pmd))) { + spin_unlock(vmf->ptl); + return 0; + } out_map: /* Restore the PMD */ pmd = pmd_modify(oldpmd, vma->vm_page_prot); @@ -1574,7 +1567,10 @@ out_map: set_pmd_at(vma->vm_mm, haddr, vmf->pmd, pmd); update_mmu_cache_pmd(vma, vmf->address, vmf->pmd); spin_unlock(vmf->ptl); - goto out; + + if (page_nid != NUMA_NO_NODE) + task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags); + return 0; }
/*