On Wed, Apr 07, 2021 at 04:35:28PM +0100, Matthew Wilcox wrote: > On Wed, Apr 07, 2021 at 04:48:44PM +0200, Peter Zijlstra wrote: > > On Tue, Apr 06, 2021 at 06:44:36PM -0700, Michel Lespinasse wrote: > > > --- a/arch/x86/mm/fault.c > > > +++ b/arch/x86/mm/fault.c > > > @@ -1219,6 +1219,8 @@ void do_user_addr_fault(struct pt_regs *regs, > > > struct mm_struct *mm; > > > vm_fault_t fault; > > > unsigned int flags = FAULT_FLAG_DEFAULT; > > > + struct vm_area_struct pvma; > > > > That's 200 bytes on-stack... I suppose that's just about acceptible, but > > perhaps we need a comment in struct vm_area_struct to make people aware > > this things lives on-stack and size really is an issue now. > > Michel's gone off and done his own thing here. I don't think that is an entirely fair representation. First we are both aware of each other's work, there is no working in dark caves here. But also, I don't even consider this patchset to be entirely my thing; most of the main building blocks come from prior proposals before mine. > The rest of us (Laurent, Liam & I) are working on top of the maple tree > which shrinks vm_area_struct by five pointers, so just 160 bytes. The idea of evaluating maple tree and speculative faults as a bundle is actually worrying to me. I think both ideas are interesting and worth looking into on their own, but I'm not convinced that they have much to do with each other. > Also, our approach doesn't involve copying VMAs in order to handle a fault. See my other reply to Peter's message - copying VMAs is a convenient way to reduce the size of the patchset, but it's not fundamental to the approach at all.
