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Subject: Re: [PATCH v2 2/2] mm/mmu_gather: send tlb_remove_table_smp_sync
 IPI only to MM CPUs
From:   ypodemsk@redhat.com
To:     Dave Hansen <dave.hansen@intel.com>, mtosatti@redhat.com,
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Date:   Mon, 26 Jun 2023 17:36:28 +0300
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         <680fadba-9104-3914-5175-e207fd3d9246@intel.com>
         <79f29f99fa07c46dbaee7b802cdd7b477b2d8dd1.camel@redhat.com>
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On Thu, 2023-06-22 at 06:37 -0700, Dave Hansen wrote:
> On 6/22/23 06:14, ypodemsk@redhat.com wrote:
> > I will send a new version with the local variable as you suggested
> > soon.
> > As for the config name, what about CONFIG_ARCH_HAS_MM_CPUMASK?
> 
> The confusing part about that name is that mm_cpumask() and
> mm->cpu_bitmap[] are defined unconditionally.  So, they're *around*
> unconditionally but just aren't updated.
> 
I think your right about the config name,
How about the
CONFIG_ARCH_USE_MM_CPUMASK?
This has the right semantic as these archs use the cpumask field of the
mm struct.

> BTW, it would also be nice to have _some_ kind of data behind this
> patch.
> 
> Fewer IPIs are better I guess, but it would still be nice if you
> could say:
> 
> 	Before this patch, /proc/interrupts showed 123 IPIs/hour for an
> 	isolated CPU.  After the approach here, it was 0.
> 
> ... or something.

This is part of an ongoing effort to remove IPIs and this one was found
via code inspection.