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From: | David Hildenbrand |
Subject: | Re: [PATCH v1 2/2] vhost: Remove vhost_backend_can_merge() callback |
Date: | Tue, 7 Mar 2023 12:24:13 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 |
On 07.03.23 12:16, Igor Mammedov wrote:
On Tue, 7 Mar 2023 11:25:48 +0100 Igor Mammedov <imammedo@redhat.com> wrote:On Thu, 16 Feb 2023 12:47:52 +0100 David Hildenbrand <david@redhat.com> wrote:Checking whether the memory regions are equal is sufficient: if they are equal, then most certainly the contained fd is equal.sounds reasonable to me.The whole vhost-user memslot handling is suboptimal and overly complicated. We shouldn't have to lookup a RAM memory regions we got notified about in vhost_user_get_mr_data() using a host pointer. But thatWhile on janitor duty can you fixup following? vhost_user_get_mr_data() -> memory_region_from_host -> -> qemu_ram_block_from_host() for qemu_ram_block_from_host doc comment seems to out of sync (ram_addr not longer exists)requires a bigger rework -- especially an alternative vhost_set_mem_table() backend call that simply consumes MemoryRegionSections.just skimming through usage of vhost_user_get_mr_data() it looks like we are first collecting MemoryRegionSection-s into tmp_sections then we do vhost_commit we convert then into vhost_memory_region list and the we are trying hard to convert addresses from the later to back to MemoryRegions we've lost during tmp_sections conversion all over the place. To me it looks like we should drop conversion to vhost_dev::mem and replace its usage with vhost_dev::mem_sections directly to get rid of data duplication and back and forth addr<->mr conversion.For now, let's just drop vhost_backend_can_merge(). Signed-off-by: David Hildenbrand <david@redhat.com>Reviewed-by: Igor Mammedov <imammedo@redhat.com>--- hw/virtio/vhost-user.c | 14 -------------- hw/virtio/vhost-vdpa.c | 1 - hw/virtio/vhost.c | 6 +----- include/hw/virtio/vhost-backend.h | 4 ---- 4 files changed, 1 insertion(+), 24 deletions(-) diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index e68daa35d4..4bfaf559a7 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -2195,19 +2195,6 @@ static int vhost_user_migration_done(struct vhost_dev *dev, char* mac_addr) return -ENOTSUP; }-static bool vhost_user_can_merge(struct vhost_dev *dev,- uint64_t start1, uint64_t size1, - uint64_t start2, uint64_t size2) -{ - ram_addr_t offset; - int mfd, rfd; - - (void)vhost_user_get_mr_data(start1, &offset, &mfd); - (void)vhost_user_get_mr_data(start2, &offset, &rfd); - - return mfd == rfd; -} - static int vhost_user_net_set_mtu(struct vhost_dev *dev, uint16_t mtu) { VhostUserMsg msg; @@ -2704,7 +2691,6 @@ const VhostOps user_ops = { .vhost_set_vring_enable = vhost_user_set_vring_enable, .vhost_requires_shm_log = vhost_user_requires_shm_log, .vhost_migration_done = vhost_user_migration_done, - .vhost_backend_can_merge = vhost_user_can_merge, .vhost_net_set_mtu = vhost_user_net_set_mtu, .vhost_set_iotlb_callback = vhost_user_set_iotlb_callback, .vhost_send_device_iotlb_msg = vhost_user_send_device_iotlb_msg, diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c index 542e003101..9ab7bc8718 100644 --- a/hw/virtio/vhost-vdpa.c +++ b/hw/virtio/vhost-vdpa.c @@ -1317,7 +1317,6 @@ const VhostOps vdpa_ops = { .vhost_set_config = vhost_vdpa_set_config, .vhost_requires_shm_log = NULL, .vhost_migration_done = NULL, - .vhost_backend_can_merge = NULL, .vhost_net_set_mtu = NULL, .vhost_set_iotlb_callback = NULL, .vhost_send_device_iotlb_msg = NULL, diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index b7fb960fa9..9d8662aa98 100644 --- a/hw/virtio/vhost.c +++ b/hw/virtio/vhost.c @@ -733,11 +733,7 @@ static void vhost_region_add_section(struct vhost_dev *dev, size_t offset = mrs_gpa - prev_gpa_start;if (prev_host_start + offset == mrs_host &&- section->mr == prev_sec->mr && - (!dev->vhost_ops->vhost_backend_can_merge || - dev->vhost_ops->vhost_backend_can_merge(dev,another question, can it relly happen, i.e. having 2 abut memory sections with the same memory region, is yes then when/why?
Unfortunately yet, because vhost relies on some hacks (sorry, but that's what it is) to make huge pages work. The following commit contains some details: commit 76525114736e8f669766e69b715fa59ce8648aae Author: Dr. David Alan Gilbert <dgilbert@redhat.com> Date: Thu Jan 16 20:24:14 2020 +0000 vhost: Only align sections for vhost-userI added hugepage alignment code in c1ece84e7c9 to deal with
vhost-user + postcopy which needs aligned pages when using userfault. However, on x86 the lower 2MB of address space tends to be shotgun'd with small fragments around the 512-640k range - e.g. video RAM, and with HyperV synic pages tend to sit around there - again splitting it up. The alignment code complains with a 'Section rounded to ...' error and gives up. Otherwise it wouldn't be needed, because flatview simplification code already merges what's reasonable. [I'll reply to you pother mail regarding that shortly] -- Thanks, David / dhildenb
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