Il giorno ven 8 apr 2022 alle ore 16:36 Ferruh Yigit <
ferruh.yigit@xilinx.com> ha scritto:

> On 4/8/2022 2:26 PM, Dmitry Kozlyuk wrote:
> > CAUTION: This message has originated from an External Source. Please use
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> responding to this email.
> >
> >
> > 2022-04-08 14:31 (UTC+0200), Antonio Di Bacco:
> >> I know that it is possible to share memory between a primary and
> secondary
> >> process using rte_memzone_reserve_aligned to allocate memory in primary
> >> that is "seen" also by the secondary. If we have two primary processes
> >> (started with different file-prefix) the same approach is not feasible.
> I
> >> wonder how to share a chunk of memory hosted on a hugepage between two
> >> primaries.
> >>
> >> Regards.
> >
> > Hi Antonio,
> >
> > Correction: all hugepages allocated by DPDK are shared
> > between primary and secondary processes, not only memzones.
> >
> > I assume we're talking about processes within one host,
> > because your previous similar question was about sharing memory between
> hosts
> > (as we have discussed offline), which is out of scope for DPDK.
> >
> > As for the question directly, you need to map the same part of the same
> file
> > in the second primary as the hugepage is mapped from in the first
> primary.
> > I don't recommend to work with file paths, because their management
> > is not straightforward (--single-file-segments, for one) and is
> undocumented.
> >
> > There is a way to share DPDK memory segment file descriptors.
> > Although public, this DPDK API is dangerous in the sense that you must
> > clearly understand what you're doing and how DPDK works.
> > Hence the question: what is the task you need this sharing for?
> > Maybe there is a simpler way.
> >
> > 1. In the first primary:
> >
> >          mz = rte_memzone_reserve()
> >          ms = rte_mem_virt2memseg(mz->addr)
> >          fd = rte_memseg_get_fd(ms)
> >          offset = rte_memseg_get_fd_offset(ms)
> >
> > 2. Use Unix domain sockets with SCM_RIGHTS
> >     to send "fd" and "offset" to the second primary.
> >
> > 3. In the second primary, after receiving "fd" and "offset":
> >
> >          flags = MAP_SHARED | MAP_HUGE | (30 << MAP_HUGE_SHIFT)
> >          addr = mmap(fd, offset, flags)
> >
> > Note that "mz" may consist of multiple "ms" depending on the sizes
> > of the zone and hugepages, and on the zone alignment.
> > Also "addr" may (and probably will) differ from "mz->addr".
> > It is possible to pass "mz->addr" and try to force it,
> > like DPDK does for primary/secondary.
> >
>
> Also 'net/memif' driver can be used:
> https://doc.dpdk.org/guides/nics/memif.html


Yes, I know about memif. Our application is currently using a chunk of
shared memory, a primary process writes on it and a secondary reads from
it.  Now the secondary will become a primary, sort of a promotion, and
MEMIF would be fine but the paradigm should change a little bit compared to
a shared memory approach.
MEMIF is an interface over a shared memory, we would need the opposite, a
shared memory over a network interface.

Thank you.