Re: [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures

[Alexander Duyck]

On 10/17/2018 12:30 AM, Mike Rapoport wrote:
> On Tue, Oct 16, 2018 at 03:01:11PM -0400, Pavel Tatashin wrote:
> > On 10/15/18 4:26 PM, Alexander Duyck wrote:
> > > This change makes it so that we use the same approach that was already in
> > > use on Sparc on all the archtectures that support a 64b long.
> > >
> > > This is mostly motivated by the fact that 8 to 10 store/move instructions
> > > are likely always going to be faster than having to call into a function
> > > that is not specialized for handling page init.
> > >
> > > An added advantage to doing it this way is that the compiler can get away
> > > with combining writes in the __init_single_page call. As a result the
> > > memset call will be reduced to only about 4 write operations, or at least
> > > that is what I am seeing with GCC 6.2 as the flags, LRU poitners, and
> > > count/mapcount seem to be cancelling out at least 4 of the 8 assignments on
> > > my system.
> > >
> > > One change I had to make to the function was to reduce the minimum page
> > > size to 56 to support some powerpc64 configurations.
> > >
> > > Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> >
> >
> > I have tested on Broadcom's Stingray cpu with 48G RAM:
> > __init_single_page() takes 19.30ns / 64-byte struct page
> > Wit the change it takes 17.33ns / 64-byte struct page
>   
> I gave it a run on an OpenPower (S812LC 8348-21C) with Power8 processor and
> with 128G of RAM. My results for 64-byte struct page were:
>
> before: 4.6788ns
> after: 4.5882ns
>
> My two cents :)

Thanks. I will add this and Pavel's data to the patch description.

- Alex