On Tue, Feb 07, 2017 at 05:33:47PM +0300, Kirill A. Shutemov wrote: > lock_pte_protection() uses pmd_lock() to make sure that we have stable > PTE page table before walking pte range. > > That's not necessary. We only need to make sure that PTE page table is > established. It cannot vanish under us as long as we hold mmap_sem at > least for read. > > And we already have helper for that -- pmd_trans_unstable(). > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > --- > mm/mprotect.c | 43 ++++++++++++------------------------------- > 1 file changed, 12 insertions(+), 31 deletions(-) > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index f9c07f54dd62..e919e4613eab 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -33,34 +33,6 @@ > > #include "internal.h" > > -/* > - * For a prot_numa update we only hold mmap_sem for read so there is a > - * potential race with faulting where a pmd was temporarily none. This > - * function checks for a transhuge pmd under the appropriate lock. It > - * returns a pte if it was successfully locked or NULL if it raced with > - * a transhuge insertion. > - */ > -static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd, > - unsigned long addr, int prot_numa, spinlock_t **ptl) > -{ > - pte_t *pte; > - spinlock_t *pmdl; > - > - /* !prot_numa is protected by mmap_sem held for write */ > - if (!prot_numa) > - return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl); > - > - pmdl = pmd_lock(vma->vm_mm, pmd); > - if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) { > - spin_unlock(pmdl); > - return NULL; > - } > - > - pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl); > - spin_unlock(pmdl); > - return pte; > -} > - > static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long addr, unsigned long end, pgprot_t newprot, > int dirty_accountable, int prot_numa) > @@ -71,7 +43,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long pages = 0; > int target_node = NUMA_NO_NODE; > > - pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl); > + pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > if (!pte) I cleaned it up too but I moved the pmd_trans_unstable in the caller above instead of the callee, otherwise it's the same. > > @@ -177,8 +149,6 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, > if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) { > if (next - addr != HPAGE_PMD_SIZE) { > __split_huge_pmd(vma, pmd, addr, false, NULL); > - if (pmd_trans_unstable(pmd)) > - continue; Agree it can be removed too, but I only removed lock_pte_protection in my version. If you prefer this version to be merged so we don't have to cleanup the above superfluous check in a incremental patch that's fine of course, otherwise at runtime they're equivalent as far as I can tell. The version in -mm is here. https://git.kernel.org/cgit/linux/kernel/git/mhocko/mm.git/commit/?h=auto-latest&id=d84ff4e4985f397ca4ecfe7ec029c45c6f2b9906 Thanks, Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>