linux-kernel - Re: [PATCH 0/5] Speed up mremap on large regions

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Message-ID: <CAJWu+oo7R6qQWz0_TnrTk_tmCfK2LgvLM-3PvhHv1wq2EyD_qg@mail.gmail.com>
Date:   Wed, 30 Sep 2020 18:46:54 -0400
From:   Joel Fernandes <joelaf@...gle.com>
To:     Lokesh Gidra <lokeshgidra@...gle.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Minchan Kim <minchan@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Hassan Naveed <hnaveed@...ecomp.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...nel.org>, Gavin Shan <gshan@...hat.com>,
        Zhenyu Ye <yezhenyu2@...wei.com>, Jia He <justin.he@....com>,
        John Hubbard <jhubbard@...dia.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Sandipan Das <sandipan@...ux.ibm.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Ram Pai <linuxram@...ibm.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Brian Geffon <bgeffon@...gle.com>,
        SeongJae Park <sjpark@...zon.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 0/5] Speed up mremap on large regions

On Wed, Sep 30, 2020 at 6:42 PM Lokesh Gidra <lokeshgidra@...gle.com> wrote:
>
> On Wed, Sep 30, 2020 at 3:32 PM Kirill A. Shutemov
> <kirill.shutemov@...ux.intel.com> wrote:
> >
> > On Wed, Sep 30, 2020 at 10:21:17PM +0000, Kalesh Singh wrote:
> > > mremap time can be optimized by moving entries at the PMD/PUD level if
> > > the source and destination addresses are PMD/PUD-aligned and
> > > PMD/PUD-sized. Enable moving at the PMD and PUD levels on arm64 and
> > > x86. Other architectures where this type of move is supported and known to
> > > be safe can also opt-in to these optimizations by enabling HAVE_MOVE_PMD
> > > and HAVE_MOVE_PUD.
> > >
> > > Observed Performance Improvements for remapping a PUD-aligned 1GB-sized
> > > region on x86 and arm64:
> > >
> > >     - HAVE_MOVE_PMD is already enabled on x86 : N/A
> > >     - Enabling HAVE_MOVE_PUD on x86   : ~13x speed up
> > >
> > >     - Enabling HAVE_MOVE_PMD on arm64 : ~ 8x speed up
> > >     - Enabling HAVE_MOVE_PUD on arm64 : ~19x speed up
> > >
> > >           Altogether, HAVE_MOVE_PMD and HAVE_MOVE_PUD
> > >           give a total of ~150x speed up on arm64.
> >
> > Is there a *real* workload that benefit from HAVE_MOVE_PUD?
> >
> We have a Java garbage collector under development which requires
> moving physical pages of multi-gigabyte heap using mremap. During this
> move, the application threads have to be paused for correctness. It is
> critical to keep this pause as short as possible to avoid jitters
> during user interaction. This is where HAVE_MOVE_PUD will greatly
> help.

And that detail should totally have gone into the commit message :-/

Thanks,

 - Joel