RE: [PATCH v3 4/5] vhost_user: support function defines for back-end

["Bathija, Pravin" <Pravin.Bathija@dell.com>]

Comments inline.


Internal Use - Confidential
> -----Original Message-----
> From: fengchengwen <fengchengwen@huawei.com>
> Sent: Tuesday, November 11, 2025 5:21 PM
> To: Bathija, Pravin <Pravin.Bathija@dell.com>; dev@dpdk.org
> Cc: pravin.m.bathija.dev@gmail.com
> Subject: Re: [PATCH v3 4/5] vhost_user: support function defines for back-end
>
>
> [EXTERNAL EMAIL]
>
> On 11/11/2025 7:31 PM, Bathija, Pravin wrote:
> > Responses inline.
> >
> >
> > Internal Use - Confidential
> >> -----Original Message-----
> >> From: fengchengwen <fengchengwen@huawei.com>
> >> Sent: Tuesday, November 4, 2025 12:06 AM
> >> To: Bathija, Pravin <Pravin.Bathija@dell.com>; dev@dpdk.org
> >> Cc: pravin.m.bathija.dev@gmail.com
> >> Subject: Re: [PATCH v3 4/5] vhost_user: support function defines for
> >> back-end
> >>
> >>
> >> [EXTERNAL EMAIL]
> >>
> >> On 11/4/2025 12:21 PM, Pravin M Bathija wrote:
> >>> Here we define support functions which are called from the various
> >>> vhost-user back-end message functions like set memory table, get
> >>> memory slots, add memory region, remove memory region.  These are
> >>> essetially common functions to initialize memory, unmap a set of
> >>> memory regions, perform register copy and align memory addresses.
> >>>
> >>> Signed-off-by: Pravin M Bathija <pravin.bathija@dell.com>
> >>> ---
> >>>  lib/vhost/vhost_user.c | 80
> >>> +++++++++++++++++++++++++++++++++++-------
> >>>  1 file changed, 68 insertions(+), 12 deletions(-)
> >>>
> >>> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c index
> >>> 168432e7d1..9a85f2fc92 100644
> >>> --- a/lib/vhost/vhost_user.c
> >>> +++ b/lib/vhost/vhost_user.c
> >>> @@ -228,7 +228,17 @@ async_dma_map(struct virtio_net *dev, bool
> >>> do_map)  }
> >>>
> >>>  static void
> >>> -free_mem_region(struct virtio_net *dev)
> >>> +free_mem_region(struct rte_vhost_mem_region *reg) {
> >>> +   if (reg != NULL && reg->host_user_addr) {
> >>> +           munmap(reg->mmap_addr, reg->mmap_size);
> >>> +           close(reg->fd);
> >>> +           memset(reg, 0, sizeof(struct rte_vhost_mem_region));
> >>> +   }
> >>> +}
> >>> +
> >>> +static void
> >>> +free_all_mem_regions(struct virtio_net *dev)
> >>>  {
> >>>     uint32_t i;
> >>>     struct rte_vhost_mem_region *reg; @@ -239,12 +249,10 @@
> >>> free_mem_region(struct virtio_net *dev)
> >>>     if (dev->async_copy && rte_vfio_is_enabled("vfio"))
> >>>             async_dma_map(dev, false);
> >>>
> >>> -   for (i = 0; i < dev->mem->nregions; i++) {
> >>> +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> >>>             reg = &dev->mem->regions[i];
> >>> -           if (reg->host_user_addr) {
> >>> -                   munmap(reg->mmap_addr, reg->mmap_size);
> >>> -                   close(reg->fd);
> >>> -           }
> >>> +           if (reg->mmap_addr)
> >>> +                   free_mem_region(reg);
> >>>     }
> >>>  }
> >>>
> >>> @@ -258,7 +266,7 @@ vhost_backend_cleanup(struct virtio_net *dev)
> >>>             vdpa_dev->ops->dev_cleanup(dev->vid);
> >>>
> >>>     if (dev->mem) {
> >>> -           free_mem_region(dev);
> >>> +           free_all_mem_regions(dev);
> >>>             rte_free(dev->mem);
> >>>             dev->mem = NULL;
> >>>     }
> >>> @@ -707,7 +715,7 @@ numa_realloc(struct virtio_net **pdev, struct
> >> vhost_virtqueue **pvq)
> >>>     vhost_devices[dev->vid] = dev;
> >>>
> >>>     mem_size = sizeof(struct rte_vhost_memory) +
> >>> -           sizeof(struct rte_vhost_mem_region) * dev->mem->nregions;
> >>> +           sizeof(struct rte_vhost_mem_region) *
> >> VHOST_MEMORY_MAX_NREGIONS;
> >>>     mem = rte_realloc_socket(dev->mem, mem_size, 0, node);
> >>>     if (!mem) {
> >>>             VHOST_CONFIG_LOG(dev->ifname, ERR, @@ -811,8 +819,10 @@
> >>> hua_to_alignment(struct rte_vhost_memory
> >> *mem, void *ptr)
> >>>     uint32_t i;
> >>>     uintptr_t hua = (uintptr_t)ptr;
> >>>
> >>> -   for (i = 0; i < mem->nregions; i++) {
> >>> +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> >>>             r = &mem->regions[i];
> >>> +           if (r->host_user_addr == 0)
> >>> +                   continue;
> >>>             if (hua >= r->host_user_addr &&
> >>>                     hua < r->host_user_addr + r->size) {
> >>>                     return get_blk_size(r->fd); @@ -1250,9 +1260,13
> >>> @@ vhost_user_postcopy_register(struct virtio_net
> >> *dev, int main_fd,
> >>>      * retrieve the region offset when handling userfaults.
> >>>      */
> >>>     memory = &ctx->msg.payload.memory;
> >>> -   for (i = 0; i < memory->nregions; i++) {
> >>> +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> >>
> >> I think the using MAX_NREGIONS are most for convienent, but it will
> >> impact the performance, because the rte_vhost_va_from_guest_pa()
> >> should iter the entire array.
> >>
> >
> > Replaced VHOST_MEMORY_MAX_NREGIONS with memory->nregions.
> Please review v4.
> >
> >> I think we should keep the original impl: make sure the nregions
> >> entry of memory-region is always valid.
> >>
> >> Beside, where is the modification for rte_vhost_va_from_guest_pa()???
> >
> > Could you please provide more detail ? rte_vhost_va_from_guest_pa() was
> never called from here before.
>
> Because rte_vhost_va_from_guest_pa() use mem-nregions as for uplimit:
>       for (i = 0; i < mem->nregions; i++) {
>
> this function was never called, but I think we need to make each commit
> complete.

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. They could be merged in unless you have some other recommendations or changes you would like me to consider. Thoughts ?

>
> >
> >>
> >>> +           int reg_msg_index = 0;
> >>>             reg = &dev->mem->regions[i];
> >>> -           memory->regions[i].userspace_addr = reg->host_user_addr;
> >>> +           if (reg->host_user_addr == 0)
> >>> +                   continue;
> >>> +           memory->regions[reg_msg_index].userspace_addr = reg-
> >>> host_user_addr;
> >>> +           reg_msg_index++;
> >>>     }
> >>>
> >>>     /* Send the addresses back to qemu */ @@ -1279,8 +1293,10 @@
> >>> vhost_user_postcopy_register(struct virtio_net *dev, int main_fd,
> >>>     }
> >>>
> >>>     /* Now userfault register and we can use the memory */
> >>> -   for (i = 0; i < memory->nregions; i++) {
> >>> +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> >>>             reg = &dev->mem->regions[i];
> >>> +           if (reg->host_user_addr == 0)
> >>> +                   continue;
> >>>             if (vhost_user_postcopy_region_register(dev, reg) < 0)
> >>>                     return -1;
> >>>     }
> >>> @@ -1385,6 +1401,46 @@ vhost_user_mmap_region(struct virtio_net
> *dev,
> >>>     return 0;
> >>>  }
> >>>
> >>> +static int
> >>> +vhost_user_initialize_memory(struct virtio_net **pdev)
> >>
> >> This function should be part of 3/5, else the 3/5 will compile fail
> >
> > I have moved support functions to patch-3. Please review v4.
> >
> >>
> >>> +{
> >>> +   struct virtio_net *dev = *pdev;
> >>> +   int numa_node = SOCKET_ID_ANY;
> >>> +
> >>> +   /*
> >>> +    * If VQ 0 has already been allocated, try to allocate on the same
> >>> +    * NUMA node. It can be reallocated later in numa_realloc().
> >>> +    */
> >>> +   if (dev->nr_vring > 0)
> >>> +           numa_node = dev->virtqueue[0]->numa_node;
> >>> +
> >>> +   dev->nr_guest_pages = 0;
> >>> +   if (dev->guest_pages == NULL) {
> >>> +           dev->max_guest_pages = 8;
> >>
> >> It should be VHOST_MEMORY_MAX_NREGIONS
> >
> > Done. Please review v4.
> >
> >>
> >>> +           dev->guest_pages = rte_zmalloc_socket(NULL,
> >>> +                                   dev->max_guest_pages *
> >>> +                                   sizeof(struct guest_page),
> >>> +                                   RTE_CACHE_LINE_SIZE,
> >>> +                                   numa_node);
> >>> +           if (dev->guest_pages == NULL) {
> >>> +                   VHOST_CONFIG_LOG(dev->ifname, ERR,
> >>> +                           "failed to allocate memory for dev-
> >>> guest_pages");
> >>> +                   return -1;
> >>> +           }
> >>> +   }
> >>> +
> >>> +   dev->mem = rte_zmalloc_socket("vhost-mem-table", sizeof(struct
> >> rte_vhost_memory) +
> >>> +           sizeof(struct rte_vhost_mem_region) *
> >> VHOST_MEMORY_MAX_NREGIONS, 0, numa_node);
> >>> +   if (dev->mem == NULL) {
> >>> +           VHOST_CONFIG_LOG(dev->ifname, ERR, "failed to allocate
> >> memory for dev->mem");
> >>> +           rte_free(dev->guest_pages);
> >>> +           dev->guest_pages = NULL;
> >>> +           return -1;
> >>> +   }
> >>> +
> >>> +   return 0;
> >>> +}
> >>> +
> >>>  static int
> >>>  vhost_user_set_mem_table(struct virtio_net **pdev,
> >>>                     struct vhu_msg_context *ctx,
> >
> >