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References: <20230228213738.272178-1-willy@infradead.org>
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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Sun, 5 Mar 2023 11:15:59 +0100
Message-ID: <CAMuHMdVD-de_jzfidbz7BQaH59=qsFVcV8wpWRfQAtdpakB0SA@mail.gmail.com>
Subject: Re: [PATCH v3 00/34] New page table range API
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     linux-mm@kvack.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Hi Willy,

On Tue, Feb 28, 2023 at 10:40 PM Matthew Wilcox (Oracle)
<willy@infradead.org> wrote:
> This patchset changes the API used by the MM to set up page table entries.
> The four APIs are:
>     set_ptes(mm, addr, ptep, pte, nr)
>     update_mmu_cache_range(vma, addr, ptep, nr)
>     flush_dcache_folio(folio)
>     flush_icache_pages(vma, page, nr)
>
> flush_dcache_folio() isn't technically new, but no architecture
> implemented it, so I've done that for you.  The old APIs remain around
> but are mostly implemented by calling the new interfaces.
>
> The new APIs are based around setting up N page table entries at once.
> The N entries belong to the same PMD, the same folio and the same VMA,
> so ptep++ is a legitimate operation, and locking is taken care of for
> you.  Some architectures can do a better job of it than just a loop,
> but I have hesitated to make too deep a change to architectures I don't
> understand well.
>
> One thing I have changed in every architecture is that PG_arch_1 is now a
> per-folio bit instead of a per-page bit.  This was something that would
> have to happen eventually, and it makes sense to do it now rather than
> iterate over every page involved in a cache flush and figure out if it
> needs to happen.
>
> The point of all this is better performance, and Fengwei Yin has
> measured improvement on x86.  I suspect you'll see improvement on
> your architecture too.  Try the new will-it-scale test mentioned here:
> https://lore.kernel.org/linux-mm/20230206140639.538867-5-fengwei.yin@intel.com/
> You'll need to run it on an XFS filesystem and have
> CONFIG_TRANSPARENT_HUGEPAGE set.

Thanks for your series!

> For testing, I've only run the code on x86.  If an x86->foo compiler
> exists in Debian, I've built defconfig.  I'm relying on the buildbots
> to tell me what I missed, and people who actually have the hardware to
> tell me if it actually works.

Seems to work fine on ARAnyM and qemu-system-m68k/virt, so
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds