On Tue, Apr 4, 2023 at 6:59 AM Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> wrote: > > The fault path will immediately fail in handle_mm_fault(), so this > is the minimal step which allows the per-VMA lock to be taken on > file-backed VMAs. There may be a small performance reduction as a > little unnecessary work will be done on each page fault. See later > patches for the improvement. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > --- > mm/memory.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index fdaec7772fff..f726f85f0081 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5223,6 +5223,9 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, > flags & FAULT_FLAG_REMOTE)) > return VM_FAULT_SIGSEGV; > > + if ((flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vma)) > + return VM_FAULT_RETRY; > + There are count_vm_event(PGFAULT) and count_memcg_event_mm(vma->vm_mm, PGFAULT) earlier in this function. Returning here and retrying I think will double-count this page fault. Returning before this accounting should fix this issue. > /* > * Enable the memcg OOM handling for faults triggered in user > * space. Kernel faults are handled more gracefully. > @@ -5275,12 +5278,8 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, > if (!vma) > goto inval; > > - /* Only anonymous vmas are supported for now */ > - if (!vma_is_anonymous(vma)) > - goto inval; > - > /* find_mergeable_anon_vma uses adjacent vmas which are not locked */ > - if (!vma->anon_vma) > + if (vma_is_anonymous(vma) && !vma->anon_vma) > goto inval; > > if (!vma_start_read(vma)) > -- > 2.39.2 >
