linux-kernel - Re: [PATCH v4 2/5] arm64: mremap speedup

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Date:   Thu, 15 Oct 2020 11:55:43 +0100
From:   Will Deacon <will@...nel.org>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     surenb@...gle.com, minchan@...gle.com, joelaf@...gle.com,
        lokeshgidra@...gle.com, kernel-team@...roid.com,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Shuah Khan <shuah@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Hassan Naveed <hnaveed@...ecomp.com>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Mark Brown <broonie@...nel.org>, Gavin Shan <gshan@...hat.com>,
        Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        Jia He <justin.he@....com>, John Hubbard <jhubbard@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ram Pai <linuxram@...ibm.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Sandipan Das <sandipan@...ux.ibm.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Brian Geffon <bgeffon@...gle.com>,
        SeongJae Park <sjpark@...zon.de>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 2/5] arm64: mremap speedup - Enable HAVE_MOVE_PMD

On Wed, Oct 14, 2020 at 12:53:07AM +0000, Kalesh Singh wrote:
> HAVE_MOVE_PMD enables remapping pages at the PMD level if both the
> source and destination addresses are PMD-aligned.
> 
> HAVE_MOVE_PMD is already enabled on x86. The original patch [1] that
> introduced this config did not enable it on arm64 at the time because
> of performance issues with flushing the TLB on every PMD move. These
> issues have since been addressed in more recent releases with
> improvements to the arm64 TLB invalidation and core mmu_gather code as
> Will Deacon mentioned in [2].
> 
> From the data below, it can be inferred that there is approximately
> 8x improvement in performance when HAVE_MOVE_PMD is enabled on arm64.
> 
> --------- Test Results ----------
> 
> The following results were obtained on an arm64 device running a 5.4
> kernel, by remapping a PMD-aligned, 1GB sized region to a PMD-aligned
> destination. The results from 10 iterations of the test are given below.
> All times are in nanoseconds.
> 
> Control    HAVE_MOVE_PMD
> 
> 9220833    1247761
> 9002552    1219896
> 9254115    1094792
> 8725885    1227760
> 9308646    1043698
> 9001667    1101771
> 8793385    1159896
> 8774636    1143594
> 9553125    1025833
> 9374010    1078125
> 
> 9100885.4  1134312.6    <-- Mean Time in nanoseconds
> 
> Total mremap time for a 1GB sized PMD-aligned region drops from
> ~9.1 milliseconds to ~1.1 milliseconds. (~8x speedup).
> 
> [1] https://lore.kernel.org/r/20181108181201.88826-3-joelaf@google.com
> [2] https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg140837.html
> 
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
> Changes in v4:
>   - Add Kirill's Acked-by.

Argh, I thought we already enabled this for PMDs back in 2018! Looks like
that we forgot to actually do that after I improved the performance of
the TLB invalidation.

I'll pick this one patch up for 5.10.

Will