Re: [dpdk-dev] [PATCH v2 2/5] mem: use address hint for mapping hugepages

[Alejandro Lucero <alejandro.lucero@netronome.com>]

On Wed, Oct 3, 2018 at 1:50 PM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:

> On 31-Aug-18 1:50 PM, Alejandro Lucero wrote:
> > Linux kernel uses a really high address as starting address for
> > serving mmaps calls. If there exist addressing limitations and
> > IOVA mode is VA, this starting address is likely too high for
> > those devices. However, it is possible to use a lower address in
> > the process virtual address space as with 64 bits there is a lot
> > of available space.
> >
> > This patch adds an address hint as starting address for 64 bits
> > systems.
> >
> > Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>
> > ---
>
> <snip>
>
> >
> >               mapped_addr = mmap(requested_addr, (size_t)map_sz,
> PROT_READ,
> >                               mmap_flags, -1, 0);
> > +
> >               if (mapped_addr == MAP_FAILED && allow_shrink)
>
> Unintended whitespace change?
>
>
Yes. I'll fix it.


> >                       *size -= page_sz;
> > -     } while (allow_shrink && mapped_addr == MAP_FAILED && *size > 0);
> > +
> > +             if (mapped_addr != MAP_FAILED && addr_is_hint &&
> > +                 mapped_addr != requested_addr) {
> > +                     /* hint was not used. Try with another offset */
> > +                     munmap(mapped_addr, map_sz);
> > +                     mapped_addr = MAP_FAILED;
> > +                     next_baseaddr = RTE_PTR_ADD(next_baseaddr,
> 0x100000000);
>
> Why not increment by page size? Sure, it could take some more time to
> allocate, but will result in less wasted memory.
>
>
I though the same or even using smaller increments than hugepage size.
Increment the address in such amount does not mean we are wasting memory
but just leaving space if some mmap fails. I think it is better to leave as
much as space as possible just in case the data allocated in the conflicted
area would need to grow in the future.


> --
> Thanks,
> Anatoly
>