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From:   "Huang\, Ying" <ying.huang@intel.com>
To:     Christopher Lameter <cl@linux.com>
Cc:     Daniel Jordan <daniel.m.jordan@oracle.com>,
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Subject: Re: Plumbers 2018 - Performance and Scalability Microconference
References: <1dc80ff6-f53f-ae89-be29-3408bf7d69cc@oracle.com>
        <01000165aa490dc9-64abf872-afd1-4a81-a46d-a50d0131de93-000000@email.amazonses.com>
Date:   Thu, 06 Sep 2018 09:58:17 +0800
In-Reply-To: <01000165aa490dc9-64abf872-afd1-4a81-a46d-a50d0131de93-000000@email.amazonses.com>
        (Christopher Lameter's message of "Wed, 5 Sep 2018 15:10:39 +0000")
Message-ID: <877ejzqtdy.fsf@yhuang-dev.intel.com>
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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.

>>  - Reducing the number of users of mmap_sem:  This semaphore is frequently
>> used throughout the kernel.  In order to facilitate scaling this longstanding
>> bottleneck, these uses should be documented and unnecessary users should be
>> fixed.
>
>
> Large page sizes also reduce contention there.

Yes.

>> If you haven't already done so, please let us know if you are interested in
>> attending, or have suggestions for other attendees.
>
> Certainly interested in attending but this overlaps supercomputing 2018 in
> Dallas Texas...

Sorry to know this.  It appears that there are too many conferences in
November...

Best Regards,
Huang, Ying