Messages in this thread | | | Date | Thu, 31 May 2018 15:50:36 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: [PATCH] mm/shmem: Zero out unused vma fields in shmem_pseudo_vma_init() |
| |
On Thu, 31 May 2018, Kirill A. Shutemov wrote:
> shmem/tmpfs uses pseudo vma to allocate page with correct NUMA policy. > > The pseudo vma doesn't have vm_page_prot set. We are going to encode > encryption KeyID in vm_page_prot. Having garbage there causes problems. > > Zero out all unused fields in the pseudo vma. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
I won't go so far as to say NAK, but personally I much prefer that we document what fields actually get used, by initializing only those, rather than having such a blanket memset.
And you say "We are going to ...": so this should really be part of some future patchset, shouldn't it?
My opinion might be in the minority: you remind me of a similar request from Josef some while ago, Cc'ing him.
(I'm very ashamed, by the way, of shmem's pseudo-vma, I think it's horrid, and just reflects that shmem was an afterthought when NUMA mempolicies were designed. Internally, we replaced alloc_pages_vma() throughout by alloc_pages_mpol(), which has no need for pseudo-vmas, and the advantage of dropping mmap_sem across the bulk of NUMA page migration. I shall be updating that work in coming months, and hope to upstream, but no promise from me on the timing - your need for vm_page_prot likely much sooner.)
Hugh
> --- > mm/shmem.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 9d6c7e595415..693fb82b4b42 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1404,10 +1404,9 @@ static void shmem_pseudo_vma_init(struct vm_area_struct *vma, > struct shmem_inode_info *info, pgoff_t index) > { > /* Create a pseudo vma that just contains the policy */ > - vma->vm_start = 0; > + memset(vma, 0, sizeof(*vma)); > /* Bias interleave by inode number to distribute better across nodes */ > vma->vm_pgoff = index + info->vfs_inode.i_ino; > - vma->vm_ops = NULL; > vma->vm_policy = mpol_shared_policy_lookup(&info->policy, index); > } > > -- > 2.17.0
| |