Re: [PATCH 2/4] mm: rmap: Allow platforms without mm_cpumask to defer TLB flush

On Fri, Jul 8, 2022 at 8:08 PM Nadav Amit [off-list ref] wrote:

On Jul 7, 2022, at 11:59 PM, Barry Song [off-list ref] wrote:

quoted

quoted

The cpumask_empty() is indeed just another memory access, which is most
likely ok. But wouldn’t adding something like CONFIG_ARCH_HAS_MM_CPUMASK
make the code simpler and (slightly, certainly slightly) more performant?

Yep. good suggestion, Nadav. So the code will be as below, right?

Hmmm… Although it is likely to work (because only x86 and arm would use this
batch flushing), I think that for consistency ARCH_HAS_MM_CPUMASK should be
correct for all architectures.

Is it really only x86 that has mm_cpumask()?

i am quite sure there are some other platforms having mm_cpumask().
for example, arm(not arm64).
but i am not exactly sure of the situation of each individual arch. thus,
i don't risk changing their source code.
but arm64 is the second platform looking for tlbbatch, and
ARCH_HAS_MM_CPUMASK only affects tlbbatch. so i would
expect those platforms to fill their ARCH_HAS_MM_CPUMASK
while they start to bringup their tlbbatch? for this moment,
we only need to make certain we don't break x86?
does it make sense?

Thanks
Barry

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