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SubjectRe: [PATCH v3 00/21] huge page clearing optimizations
On Wed, Jun 8, 2022 at 12:25 PM Ankur Arora <ankur.a.arora@oracle.com> wrote:
>
> But, even on x86, AFAICT gigantic pages could straddle MAX_SECTION_BITS?
> An arch specific clear_huge_page() code could, however handle 1GB pages
> via some kind of static loop around (30 - MAX_SECTION_BITS).

Even if gigantic pages straddle that area, it simply shouldn't matter.

The only reason that MAX_SECTION_BITS matters is for the 'struct page *' lookup.

And the only reason for *that* is because of HIGHMEM.

So it's all entirely silly and pointless on any sane architecture, I think.

> We'll need a preemption point there for CONFIG_PREEMPT_VOLUNTARY
> as well, right?

Ahh, yes. I should have looked at the code, and not just gone by my
"PREEMPT_NONE vs PREEMPT" thing that entirely forgot about how we
split that up.

> Just one minor point -- seems to me that the choice of nontemporal or
> temporal might have to be based on a hint to clear_huge_page().

Quite possibly. But I'd prefer that as a separate "look, this
improves numbers by X%" thing from the whole "let's make the
clear_huge_page() interface at least sane".

Linus

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