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From:   Hugh Dickins <hughd@google.com>
Date:   Thu, 6 Sep 2018 17:52:53 -0700
Message-ID: <CANsGZ6bW0vJcRpnfAesH-9_9vnrrvMHYH-UjH50zqLtA4WALyg@mail.gmail.com>
Subject: Re: Plumbers 2018 - Performance and Scalability Microconference
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     "Huang, Ying" <ying.huang@intel.com>,
        Christoph Lameter <cl@linux.com>, daniel.m.jordan@oracle.com,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, aaron.lu@intel.com,
        alex.kogan@oracle.com, Andrew Morton <akpm@linux-foundation.org>,
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        Davidlohr Bueso <dave@stgolabs.net>, dave.dice@oracle.com,
        dhaval.giani@oracle.com, ktkhai@virtuozzo.com,
        Laurent Dufour <ldufour@linux.vnet.ibm.com>,
        Pavel.Tatashin@microsoft.com,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@intel.com>,
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        Steven Sistare <steven.sistare@oracle.com>,
        Jonathan Adams <jwadams@google.com>,
        Ashwin Chaugule <ashwinch@google.com>,
        Salman Qazi <sqazi@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Michel Lespinasse <walken@google.com>,
        David Rientjes <rientjes@google.com>,
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        Neha Agarwal <nehaagarwal@google.com>,
        Greg Thelen <gthelen@google.com>
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On Thu, Sep 6, 2018 at 2:36 PM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 09/05/2018 06:58 PM, Huang, Ying wrote:
> > Hi, Christopher,
> >
> > Christopher Lameter <cl@linux.com> writes:
> >
> >> On Tue, 4 Sep 2018, Daniel Jordan wrote:
> >>
> >>>  - Promoting huge page usage:  With memory sizes becoming ever larger, huge
> >>> pages are becoming more and more important to reduce TLB misses and the
> >>> overhead of memory management itself--that is, to make the system scalable
> >>> with the memory size.  But there are still some remaining gaps that prevent
> >>> huge pages from being deployed in some situations, such as huge page
> >>> allocation latency and memory fragmentation.
> >>
> >> You forgot the major issue that huge pages in the page cache are not
> >> supported and thus we have performance issues with fast NVME drives that
> >> are now able to do 3Gbytes per sec that are only possible to reach with
> >> directio and huge pages.
> >
> > Yes.  That is an important gap for huge page.  Although we have huge
> > page cache support for tmpfs, we lacks that for normal file systems.
> >
> >> IMHO the huge page issue is just the reflection of a certain hardware
> >> manufacturer inflicting pain for over a decade on its poor users by not
> >> supporting larger base page sizes than 4k. No such workarounds needed on
> >> platforms that support large sizes. Things just zoom along without
> >> contortions necessary to deal with huge pages etc.
> >>
> >> Can we come up with a 2M base page VM or something? We have possible
> >> memory sizes of a couple TB now. That should give us a million or so 2M
> >> pages to work with.
> >
> > That sounds a good idea.  Don't know whether someone has tried this.
>
> IIRC, Hugh Dickins and some others at Google tried going down this path.
> There was a brief discussion at LSF/MM.  It is something I too would like
> to explore in my spare time.

Almost: I never tried that path myself, but mentioned that Greg Thelen had.

Hugh