Re: [dpdk-dev] [PATCH v2] mem: limit use of address hint

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

On Tue, Apr 2, 2019 at 5:13 PM Burakov, Anatoly <anatoly.burakov@intel.com>
wrote:

> On 31-Mar-19 9:43 AM, Shahaf Shuler wrote:
> > patch[1] added an address hint as starting address for 64 bit systems in
> > case an explicit base virtual address was not set by the user.
> >
> > The justification for such hint was to help devices that work in VA
> > mode and has a address range limitation to work smoothly with the eal
> > memory subsystem.
> >
> > While the base address value selected may work fine for the eal
> > initialization, it easily breaks when trying to register external memory
> > using rte_extmem_register API.
> >
> > Trying to register anonymous memory on RH x86_64 machine took several
> > minutes, during them the function eal_get_virtual_area repeatedly
> > scanned for a good VA candidate.
> >
> > The attempt to guess which VA address will be free for mapping will
> > always result in not portable, error prone code:
> > * different application may use different libraries along w/ DPDK. One
> >    can never guess which library was called first and how much virtual
> >    memory it consumed.
> > * external memory can be registered at any time in the application run
> >    time.
> >
> > In order not to break the existing secondary process design, this patch
> > only limits the max number of tries that will be done with the
> > address hint.
> > When the number of tries exceeds the threshold the code
> > will use the suggested address from kernel.
> >
> > Fixes: 1df21702873d ("mem: use address hint for mapping hugepages")
> > Cc: stable@dpdk.org
> > Cc: alejandro.lucero@netronome.com
> >
> > [1] commit 1df21702873d ("mem: use address hint for mapping hugepages")
> >
> > Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
> > ---
> >
> > On v2:
> >   * instead of a complete remove of the hint limit the number of tries
> we allow.
> > ---
>
> LGTM
>
> Tested-by: Anatoly Burakov <anatoly.burakov@intel.com>
>
> We can always increase the number of tries later :)
>
>
This is also fine for me.
If the map address is not within the supported range by a device with
addressing limitations, the device will not be used.
Not sure how this is likely to happen, but I guess if it is become a
problem, another solution should be implemented.

Acked-by: Alejandro Lucero <alejandro.lucero@netronome.com>



> --
> Thanks,
> Anatoly
>