[PATCH v3 5/5] vhost_user: Increase number of memory regions

[Bathija, Pravin]

Responses inline.


Internal Use - Confidential
> -----Original Message-----
> From: fengchengwen <fengchengwen at huawei.com>
> Sent: Wednesday, November 12, 2025 11:23 PM
> To: Bathija, Pravin <Pravin.Bathija at dell.com>; dev at dpdk.org
> Cc: pravin.m.bathija.dev at gmail.com
> Subject: Re: [PATCH v3 5/5] vhost_user: Increase number of memory regions
>
>
> [EXTERNAL EMAIL]
>
> On 11/13/2025 10:13 AM, Bathija, Pravin wrote:
> > Answers inline
> >
> >
> > Internal Use - Confidential
> >> -----Original Message-----
> >> From: fengchengwen <fengchengwen at huawei.com>
> >> Sent: Tuesday, November 11, 2025 5:26 PM
> >> To: Bathija, Pravin <Pravin.Bathija at dell.com>; dev at dpdk.org
> >> Cc: pravin.m.bathija.dev at gmail.com
> >> Subject: Re: [PATCH v3 5/5] vhost_user: Increase number of memory
> >> regions
> >>
> >>
> >> [EXTERNAL EMAIL]
> >>
> >> On 11/11/2025 7:34 PM, Bathija, Pravin wrote:
> >>> Responses inline.
> >>>
> >>>
> >>> Internal Use - Confidential
> >>>> -----Original Message-----
> >>>> From: fengchengwen <fengchengwen at huawei.com>
> >>>> Sent: Tuesday, November 4, 2025 12:12 AM
> >>>> To: Bathija, Pravin <Pravin.Bathija at dell.com>; dev at dpdk.org
> >>>> Cc: pravin.m.bathija.dev at gmail.com
> >>>> Subject: Re: [PATCH v3 5/5] vhost_user: Increase number of memory
> >>>> regions
> >>>>
> >>>>
> >>>> [EXTERNAL EMAIL]
> >>>>
> >>>> On 11/4/2025 12:21 PM, Pravin M Bathija wrote:
> >>>>> In this patch the number of memory regions are increased from
> >>>>> 8 to 128. When a vhost-user front-end such as qemu or libblkio
> >>>>> queries the back-end such as dpdk with the message, get max number
> >>>>> of memory slots, the back-end replies with this number 128 instead
> >>>>> of the previously defined 8. The back-end also allocates that many
> >>>>> slots in the memory table where regions are added/removed as
> >>>>> requested by the vhost-user front-end. This also helps the vhost-
> >>>>> user front-end to limit the number of memory regions when sending
> >>>>> the set mem table message ar adding memory regions.
> >>>>>
> >>>>> Signed-off-by: Pravin M Bathija <pravin.bathija at dell.com>
> >>>>> ---
> >>>>>  lib/vhost/vhost_user.h | 2 +-
> >>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/lib/vhost/vhost_user.h b/lib/vhost/vhost_user.h index
> >>>>> 5a0e747b58..c6ad5b76d6 100644
> >>>>> --- a/lib/vhost/vhost_user.h
> >>>>> +++ b/lib/vhost/vhost_user.h
> >>>>> @@ -11,7 +11,7 @@
> >>>>>
> >>>>>  /* refer to hw/virtio/vhost-user.c */
> >>>>>
> >>>>> -#define VHOST_MEMORY_MAX_NREGIONS 8
> >>>>> +#define VHOST_MEMORY_MAX_NREGIONS 128
> >>>>
> >>>> The address translation may increase a lot if the real region is 128.
> >>>> Maybe we should add another patch to optimize it.
> >>>
> >>> Could you please share more thoughts on this ?  Are you concerned
> >>> about
> >> the number of addresses and translation table bloat ? What
> >> optimization are you suggesting ?
> >>
> >> Because each memory region is independent and does not overlap, maybe
> >> we could use binary search to optimize it.
> >
> > From what I gather, both of your latest comments, for patches 4 and 5 are
> related to performance impact because of 128 memory regions. My thoughts
> on this are, I will work on an algorithm to optimize as you suggested.
> Meanwhile we could approve patches 1-4. The rest of the implementation does
> not need 128 memory regions. The existing 8 regions are fine. I put in this
> change as I felt it makes the system scale more and was also suggested by
> Maxime. I think patches 1-4 stand by themselves and have been thoroughly
> tested. Please let me know your thoughts on this.
>
> I am OK for this.

Thank you for the quick response. I have just submitted v5 of the patchset where I removed the patch which increases the memory regions to 128. Please Ack and help merge to mainline.

>
> >
> >>
> >>>
> >>>>
> >>>>>
> >>>>>  #define VHOST_USER_NET_SUPPORTED_FEATURES \
> >>>>>     (VIRTIO_NET_SUPPORTED_FEATURES | \
> >>>
> >>>
> >
> >