Re: [PATCH v6 1/9] mm: x86, arm64: add arch_has_hw_pte_young()

[Yu Zhao]

On Tue, Jan 11, 2022 at 02:19:02PM +0000, Will Deacon wrote:
> On Fri, Jan 07, 2022 at 12:25:07AM -0700, Yu Zhao wrote:
> > On Thu, Jan 06, 2022 at 10:30:09AM +0000, Will Deacon wrote:
> > > On Wed, Jan 05, 2022 at 01:47:08PM -0700, Yu Zhao wrote:
> > > > On Wed, Jan 05, 2022 at 10:45:26AM +0000, Will Deacon wrote:
> > > > > On Tue, Jan 04, 2022 at 01:22:20PM -0700, Yu Zhao wrote:
> > > > > > diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> > > > > > index 870c39537dd0..56e4ef5d95fa 100644
> > > > > > --- a/arch/arm64/tools/cpucaps
> > > > > > +++ b/arch/arm64/tools/cpucaps
> > > > > > @@ -36,6 +36,7 @@ HAS_STAGE2_FWB
> > > > > >  HAS_SYSREG_GIC_CPUIF
> > > > > >  HAS_TLB_RANGE
> > > > > >  HAS_VIRT_HOST_EXTN
> > > > > > +HW_AF
> > > > > >  HW_DBM
> > > > > >  KVM_PROTECTED_MODE
> > > > > >  MISMATCHED_CACHE_TYPE
> > > > > 
> > > > > As discussed in the previous threads, we really don't need the complexity
> > > > > of the additional cap for the arm64 part. Please can you just use the
> > > > > existing code instead? It's both simpler and, as you say, it's equivalent
> > > > > for existing hardware.
> > > > > 
> > > > > That way, this patch just ends up being a renaming exercise and we're all
> > > > > good.
> > > > 
> > > > No, renaming alone isn't enough. A caller needs to disable preemption
> > > > before calling system_has_hw_af(), and I don't think it's reasonable
> > > > to ask this caller to do it on x86 as well.
> > > > 
> > > > It seems you really prefer not to have HW_AF. So the best I can
> > > > accommodate, considering other potential archs, e.g., risc-v (I do
> > > > plan to provide benchmark results on risc-v, btw), is:
> > > > 
> > > >   static inline bool arch_has_hw_pte_young(bool local)
> > > >   {
> > > > 	bool hw_af;
> > > > 
> > > >   	if (local) {
> > > >   		WARN_ON(preemptible());
> > > >   		return cpu_has_hw_af();
> > > >   	}
> > > >   
> > > > 	preempt_disable();
> > > >   	hw_af = system_has_hw_af();
> > > > 	preempt_enable();
> > > > 
> > > > 	return hw_af;
> > > >   }
> > > > 
> > > > Or please give me something else I can call without disabling
> > > > preemption, sounds good?
> > > 
> > > Sure thing, let me take a look. Do you have your series on a public git
> > > tree someplace?
> > 
> > Thanks!
> > 
> > This patch (updated) on Gerrit:
> > https://linux-mm-review.googlesource.com/c/page-reclaim/+/1500/1
> 
> How about folding in something like the diff below? I've basically removed
> that 'bool local' argument and dropped the preemptible() check from the
> arm64 code.

This looks great, thanks.