mm/numa: no task_numa_fault() call if PMD is changed

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.com/
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>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5f32a196a612efe3de6e7505c3ae34266715fd9b..4d9c1277e5e4d14c7d22e6afb1328e430ff8148d 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1672,7 +1672,7 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
        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);
@@ -1715,22 +1715,16 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
        if (!migrate_misplaced_folio(folio, vma, target_nid)) {
                flags |= TNF_MIGRATED;
                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;
-       }
-
-out:
-       if (nid != NUMA_NO_NODE)
                task_numa_fault(last_cpupid, nid, HPAGE_PMD_NR, flags);
+               return 0;
+       }
 
-       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);
@@ -1740,7 +1734,10 @@ 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 (nid != NUMA_NO_NODE)
+               task_numa_fault(last_cpupid, nid, HPAGE_PMD_NR, flags);
+       return 0;
 }
 
 /*