On Thu, May 31, 2018 at 10:50:36PM +0000, Hugh Dickins wrote: > 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@xxxxxxxxxxxxxxx> > > 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. I recognize value of documentation here. But I still think leaving garbage in the fields is not a great idea. > > And you say "We are going to ...": so this should really be part of > some future patchset, shouldn't it? Yeah. It's for MKTME. I just try to push easy patches first. > 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.) I will try to look at how we can get alloc_pages_mpol() implemented. (Although interleave bias is kinda confusing. I'll need to wrap my head around the thing.) -- Kirill A. Shutemov
