Re: Plumbers 2018 - Performance and Scalability Microconference

[Hugh Dickins <hughd@google.com>]

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