On Tue, Jan 12, 2021 at 09:43:38PM +0000, Will Deacon wrote: > On Tue, Jan 12, 2021 at 12:38:34PM -0800, Nadav Amit wrote: > > > On Jan 12, 2021, at 11:56 AM, Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > > On Tue, Jan 12, 2021 at 11:15:43AM -0800, Nadav Amit wrote: > > >> I will send an RFC soon for per-table deferred TLB flushes tracking. > > >> The basic idea is to save a generation in the page-struct that tracks > > >> when deferred PTE change took place, and track whenever a TLB flush > > >> completed. In addition, other users - such as mprotect - would use > > >> the tlb_gather interface. > > >> > > >> Unfortunately, due to limited space in page-struct this would only > > >> be possible for 64-bit (and my implementation is only for x86-64). > > > > > > I don't want to discourage you but I don't think this would end up > > > well. PPC doesn't necessarily follow one-page-struct-per-table rule, > > > and I've run into problems with this before while trying to do > > > something similar. > > > > Discourage, discourage. Better now than later. > > > > It will be relatively easy to extend the scheme to be per-VMA instead of > > per-table for architectures that prefer it this way. It does require > > TLB-generation tracking though, which Andy only implemented for x86, so I > > will focus on x86-64 right now. > > Can you remind me of what we're missing on arm64 in this area, please? I'm > happy to help get this up and running once you have something I can build > on. I noticed arm/arm64 don't support ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH. Would it be something worth pursuing? Arm has been using mm_cpumask, so it might not be too difficult I guess?
