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SubjectRe: Plumbers 2018 - Performance and Scalability Microconference
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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

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