[dpdk-dev] [PATCH v2 2/5] mem: use address hint for mapping hugepages
Burakov, Anatoly
anatoly.burakov at intel.com
Thu Oct 4 14:08:26 CEST 2018
On 04-Oct-18 12:43 PM, Alejandro Lucero wrote:
>
>
> On Wed, Oct 3, 2018 at 1:50 PM Burakov, Anatoly
> <anatoly.burakov at intel.com <mailto:anatoly.burakov at 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 at netronome.com
> <mailto:alejandro.lucero at 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.
Not sure i follow. Could you give an example of a scenario where leaving
huge chunks of memory free would be preferable to just adding page size
and starting from page-size-aligned address next time we allocate?
>
> --
> Thanks,
> Anatoly
>
--
Thanks,
Anatoly
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