Re: [PATCH 3/3] net/virtio-user: fix memory hotplug support in vhost-kernel

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 07-Sep-18 12:37 PM, Tiwei Bie wrote:
> On Fri, Sep 07, 2018 at 10:44:22AM +0100, Burakov, Anatoly wrote:
>> On 05-Sep-18 5:28 AM, Tiwei Bie wrote:
>>> It's possible to have much more hugepage backed memory regions
>>> than what vhost-kernel supports due to the memory hotplug, which
>>> may cause problems. A better solution is to have the virtio-user
>>> pass all the memory ranges reserved by DPDK to vhost-kernel.
>>>
>>> Fixes: 12ecb2f63b12 ("net/virtio-user: support memory hotplug")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>> ---
>>>    drivers/net/virtio/virtio_user/vhost_kernel.c | 38 +++++++++----------
>>>    1 file changed, 18 insertions(+), 20 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio/virtio_user/vhost_kernel.c b/drivers/net/virtio/virtio_user/vhost_kernel.c
>>> index 897fee0af..9338166d9 100644
>>> --- a/drivers/net/virtio/virtio_user/vhost_kernel.c
>>> +++ b/drivers/net/virtio/virtio_user/vhost_kernel.c
>>> @@ -70,41 +70,41 @@ static uint64_t vhost_req_user_to_kernel[] = {
>>>    	[VHOST_USER_SET_MEM_TABLE] = VHOST_SET_MEM_TABLE,
>>>    };
>>> -struct walk_arg {
>>> -	struct vhost_memory_kernel *vm;
>>> -	uint32_t region_nr;
>>> -};
>>>    static int
>>> -add_memory_region(const struct rte_memseg_list *msl __rte_unused,
>>> -		const struct rte_memseg *ms, size_t len, void *arg)
>>> +add_memseg_list(const struct rte_memseg_list *msl, void *arg)
>>>    {
>>> -	struct walk_arg *wa = arg;
>>> +	struct vhost_memory_kernel *vm = arg;
>>>    	struct vhost_memory_region *mr;
>>>    	void *start_addr;
>>> +	uint64_t len;
>>> -	if (wa->region_nr >= max_regions)
>>> +	if (vm->nregions >= max_regions)
>>>    		return -1;
>>> -	mr = &wa->vm->regions[wa->region_nr++];
>>> -	start_addr = ms->addr;
>>> +	start_addr = msl->base_va;
>>> +	len = msl->page_sz * msl->memseg_arr.len;
>>> +
>>> +	mr = &vm->regions[vm->nregions++];
>>>    	mr->guest_phys_addr = (uint64_t)(uintptr_t)start_addr;
>>>    	mr->userspace_addr = (uint64_t)(uintptr_t)start_addr;
>>>    	mr->memory_size = len;
>>> -	mr->mmap_offset = 0;
>>> +	mr->mmap_offset = 0; /* flags_padding */
>>> +
>>> +	PMD_DRV_LOG(DEBUG, "index=%u addr=%p len=%" PRIu64,
>>> +			vm->nregions - 1, start_addr, len);
>>>    	return 0;
>>>    }
>>> -/* By default, vhost kernel module allows 64 regions, but DPDK allows
>>> - * 256 segments. As a relief, below function merges those virtually
>>> - * adjacent memsegs into one region.
>>> +/* By default, vhost kernel module allows 64 regions, but DPDK may
>>> + * have much more memory regions. Below function will treat each
>>> + * contiguous memory space reserved by DPDK as one region.
>>>     */
>>>    static struct vhost_memory_kernel *
>>>    prepare_vhost_memory_kernel(void)
>>>    {
>>>    	struct vhost_memory_kernel *vm;
>>> -	struct walk_arg wa;
>>>    	vm = malloc(sizeof(struct vhost_memory_kernel) +
>>>    			max_regions *
>>> @@ -112,20 +112,18 @@ prepare_vhost_memory_kernel(void)
>>>    	if (!vm)
>>>    		return NULL;
>>> -	wa.region_nr = 0;
>>> -	wa.vm = vm;
>>> +	vm->nregions = 0;
>>> +	vm->padding = 0;
>>>    	/*
>>>    	 * The memory lock has already been taken by memory subsystem
>>>    	 * or virtio_user_start_device().
>>>    	 */
>>> -	if (rte_memseg_contig_walk_thread_unsafe(add_memory_region, &wa) < 0) {
>>> +	if (rte_memseg_list_walk_thread_unsafe(add_memseg_list, vm) < 0) {
>>>    		free(vm);
>>>    		return NULL;
>>>    	}
>>> -	vm->nregions = wa.region_nr;
>>> -	vm->padding = 0;
>>>    	return vm;
>>>    }
>>>
>>
>> Doesn't that assume single file segments mode?
> 
> This is to find out the VA ranges reserved by memory subsystem.
> Why does it need to assume single file segments mode?

If you are not in single-file segments mode, each individual page in a 
VA-contiguous area will be behind a different fd - so it will be part of 
a different region, would it not?

> 
> 
>>
>> -- 
>> Thanks,
>> Anatoly
> 


-- 
Thanks,
Anatoly