diff options
| author | John Hubbard <jhubbard@nvidia.com> | 2024-02-27 19:41:51 -0800 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-03-04 17:01:27 -0800 |
| commit | 6c1b748ebf27befffec83b77ca1960bf70ed6ac9 (patch) | |
| tree | f7f95f3c4d79bb6e47a2c89d41a59a553ce6d51d /mm/memory.c | |
| parent | c8b36003121834cb77fcaf8a1ce0a454d7a97891 (diff) | |
mm/memory.c: do_numa_page(): remove a redundant page table read
do_numa_page() is reading from the same page table entry, twice, while
holding the page table lock: once while checking that the pte hasn't
changed, and again in order to modify the pte.
Instead, just read the pte once, and save it in the same old_pte variable
that already exists. This has no effect on behavior, other than to
provide a tiny potential improvement to performance, by avoiding the
redundant memory read (which the compiler cannot elide, due to
READ_ONCE()).
Also improve the associated comments nearby.
Link: https://lkml.kernel.org/r/20240228034151.459370-1-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
| -rw-r--r-- | mm/memory.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/mm/memory.c b/mm/memory.c index 75e0abda8642..230bcd12a336 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5127,18 +5127,18 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) int flags = 0; /* - * The "pte" at this point cannot be used safely without - * validation through pte_unmap_same(). It's of NUMA type but - * the pfn may be screwed if the read is non atomic. + * The pte cannot be used safely until we verify, while holding the page + * table lock, that its contents have not changed during fault handling. */ spin_lock(vmf->ptl); - if (unlikely(!pte_same(ptep_get(vmf->pte), vmf->orig_pte))) { + /* Read the live PTE from the page tables: */ + old_pte = ptep_get(vmf->pte); + + if (unlikely(!pte_same(old_pte, vmf->orig_pte))) { pte_unmap_unlock(vmf->pte, vmf->ptl); goto out; } - /* Get the normal PTE */ - old_pte = ptep_get(vmf->pte); pte = pte_modify(old_pte, vma->vm_page_prot); /* |