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

[Bathija, Pravin]

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.

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