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Subject: Re: Plumbers 2018 - Performance and Scalability Microconference
To:     "Huang, Ying" <ying.huang@intel.com>,
        Christopher Lameter <cl@linux.com>
Cc:     Daniel Jordan <daniel.m.jordan@oracle.com>,
        linux-kernel@vger.kernel.org,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Aaron Lu <aaron.lu@intel.com>, alex.kogan@oracle.com,
        akpm@linux-foundation.org, boqun.feng@gmail.com, brouer@redhat.com,
        dave@stgolabs.net, dave.dice@oracle.com,
        Dhaval Giani <dhaval.giani@oracle.com>, ktkhai@virtuozzo.com,
        ldufour@linux.vnet.ibm.com, Pavel.Tatashin@microsoft.com,
        paulmck@linux.vnet.ibm.com, shady.issa@oracle.com,
        tariqt@mellanox.com, tglx@linutronix.de, tim.c.chen@intel.com,
        vbabka@suse.cz, longman@redhat.com, yang.shi@linux.alibaba.com,
        shy828301@gmail.com, subhra.mazumdar@oracle.com,
        Steven Sistare <steven.sistare@oracle.com>, jwadams@google.com,
        ashwinch@google.com, sqazi@google.com,
        Shakeel Butt <shakeelb@google.com>, walken@google.com,
        rientjes@google.com, junaids@google.com,
        Neha Agarwal <nehaagarwal@google.com>,
        Hugh Dickins <hughd@google.com>
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From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <bd6f6f8b-4880-6c20-62f5-bb6ca3b5e6f7@oracle.com>
Date:   Thu, 6 Sep 2018 14:36:38 -0700
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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.

-- 
Mike Kravetz