Re: [Qemu-devel] [PATCH] exec: separate sections and nodes per address space

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Dec 01, 2013 at 02:02:23PM +0200, Marcel Apfelbaum wrote:
> Every address space has its own nodes and sections, but
> it uses the same global arrays of nodes/section.
> 
> This limits the number of devices that can be attached
> to the guest to 20-30 devices. It happens because:
>  - The sections array is limited to 2^12 entries.
>  - The main memory has at least 100 sections.
>  - Each device address space is actually an alias to
>    main memory, multiplying its number of nodes/sections.
> 
> Remove the limitation by using separate arrays of
> nodes and sections for each address space.
> 
> Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

I think this is actually needed for stable branches:
this failure to support large number of devices is
a regression since 1.3.0

Cc: qemu-stable@nongnu.org

> ---
>  exec.c | 151 ++++++++++++++++++++++++++++-------------------------------------
>  1 file changed, 64 insertions(+), 87 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 95c4356..db2844c 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -90,13 +90,21 @@ struct PhysPageEntry {
>  
>  typedef PhysPageEntry Node[L2_SIZE];
>  
> +typedef struct PhysPageMap {
> +    unsigned sections_nb;
> +    unsigned sections_nb_alloc;
> +    unsigned nodes_nb;
> +    unsigned nodes_nb_alloc;
> +    Node *nodes;
> +    MemoryRegionSection *sections;
> +} PhysPageMap;
> +
>  struct AddressSpaceDispatch {
>      /* This is a multi-level map on the physical address space.
>       * The bottom level has pointers to MemoryRegionSections.
>       */
>      PhysPageEntry phys_map;
> -    Node *nodes;
> -    MemoryRegionSection *sections;
> +    PhysPageMap map;
>      AddressSpace *as;
>  };
>  
> @@ -113,18 +121,6 @@ typedef struct subpage_t {
>  #define PHYS_SECTION_ROM 2
>  #define PHYS_SECTION_WATCH 3
>  
> -typedef struct PhysPageMap {
> -    unsigned sections_nb;
> -    unsigned sections_nb_alloc;
> -    unsigned nodes_nb;
> -    unsigned nodes_nb_alloc;
> -    Node *nodes;
> -    MemoryRegionSection *sections;
> -} PhysPageMap;
> -
> -static PhysPageMap *prev_map;
> -static PhysPageMap next_map;
> -
>  #define PHYS_MAP_NODE_NIL (((uint16_t)~0) >> 1)
>  
>  static void io_mem_init(void);
> @@ -135,35 +131,32 @@ static MemoryRegion io_mem_watch;
>  
>  #if !defined(CONFIG_USER_ONLY)
>  
> -static void phys_map_node_reserve(unsigned nodes)
> +static void phys_map_node_reserve(PhysPageMap *map, unsigned nodes)
>  {
> -    if (next_map.nodes_nb + nodes > next_map.nodes_nb_alloc) {
> -        next_map.nodes_nb_alloc = MAX(next_map.nodes_nb_alloc * 2,
> -                                            16);
> -        next_map.nodes_nb_alloc = MAX(next_map.nodes_nb_alloc,
> -                                      next_map.nodes_nb + nodes);
> -        next_map.nodes = g_renew(Node, next_map.nodes,
> -                                 next_map.nodes_nb_alloc);
> +    if (map->nodes_nb + nodes > map->nodes_nb_alloc) {
> +        map->nodes_nb_alloc = MAX(map->nodes_nb_alloc * 2, 16);
> +        map->nodes_nb_alloc = MAX(map->nodes_nb_alloc, map->nodes_nb + nodes);
> +        map->nodes = g_renew(Node, map->nodes, map->nodes_nb_alloc);
>      }
>  }
>  
> -static uint16_t phys_map_node_alloc(void)
> +static uint16_t phys_map_node_alloc(PhysPageMap *map)
>  {
>      unsigned i;
>      uint16_t ret;
>  
> -    ret = next_map.nodes_nb++;
> +    ret = map->nodes_nb++;
>      assert(ret != PHYS_MAP_NODE_NIL);
> -    assert(ret != next_map.nodes_nb_alloc);
> +    assert(ret != map->nodes_nb_alloc);
>      for (i = 0; i < L2_SIZE; ++i) {
> -        next_map.nodes[ret][i].is_leaf = 0;
> -        next_map.nodes[ret][i].ptr = PHYS_MAP_NODE_NIL;
> +        map->nodes[ret][i].is_leaf = 0;
> +        map->nodes[ret][i].ptr = PHYS_MAP_NODE_NIL;
>      }
>      return ret;
>  }
>  
> -static void phys_page_set_level(PhysPageEntry *lp, hwaddr *index,
> -                                hwaddr *nb, uint16_t leaf,
> +static void phys_page_set_level(PhysPageMap *map, PhysPageEntry *lp,
> +                                hwaddr *index, hwaddr *nb, uint16_t leaf,
>                                  int level)
>  {
>      PhysPageEntry *p;
> @@ -171,8 +164,8 @@ static void phys_page_set_level(PhysPageEntry *lp, hwaddr *index,
>      hwaddr step = (hwaddr)1 << (level * L2_BITS);
>  
>      if (!lp->is_leaf && lp->ptr == PHYS_MAP_NODE_NIL) {
> -        lp->ptr = phys_map_node_alloc();
> -        p = next_map.nodes[lp->ptr];
> +        lp->ptr = phys_map_node_alloc(map);
> +        p = map->nodes[lp->ptr];
>          if (level == 0) {
>              for (i = 0; i < L2_SIZE; i++) {
>                  p[i].is_leaf = 1;
> @@ -180,7 +173,7 @@ static void phys_page_set_level(PhysPageEntry *lp, hwaddr *index,
>              }
>          }
>      } else {
> -        p = next_map.nodes[lp->ptr];
> +        p = map->nodes[lp->ptr];
>      }
>      lp = &p[(*index >> (level * L2_BITS)) & (L2_SIZE - 1)];
>  
> @@ -191,7 +184,7 @@ static void phys_page_set_level(PhysPageEntry *lp, hwaddr *index,
>              *index += step;
>              *nb -= step;
>          } else {
> -            phys_page_set_level(lp, index, nb, leaf, level - 1);
> +            phys_page_set_level(map, lp, index, nb, leaf, level - 1);
>          }
>          ++lp;
>      }
> @@ -202,9 +195,9 @@ static void phys_page_set(AddressSpaceDispatch *d,
>                            uint16_t leaf)
>  {
>      /* Wildly overreserve - it doesn't matter much. */
> -    phys_map_node_reserve(3 * P_L2_LEVELS);
> +    phys_map_node_reserve(&d->map, 3 * P_L2_LEVELS);
>  
> -    phys_page_set_level(&d->phys_map, &index, &nb, leaf, P_L2_LEVELS - 1);
> +    phys_page_set_level(&d->map, &d->phys_map, &index, &nb, leaf, P_L2_LEVELS - 1);
>  }
>  
>  static MemoryRegionSection *phys_page_find(PhysPageEntry lp, hwaddr index,
> @@ -237,10 +230,10 @@ static MemoryRegionSection *address_space_lookup_region(AddressSpaceDispatch *d,
>      subpage_t *subpage;
>  
>      section = phys_page_find(d->phys_map, addr >> TARGET_PAGE_BITS,
> -                             d->nodes, d->sections);
> +                             d->map.nodes, d->map.sections);
>      if (resolve_subpage && section->mr->subpage) {
>          subpage = container_of(section->mr, subpage_t, iomem);
> -        section = &d->sections[subpage->sub_section[SUBPAGE_IDX(addr)]];
> +        section = &d->map.sections[subpage->sub_section[SUBPAGE_IDX(addr)]];
>      }
>      return section;
>  }
> @@ -708,7 +701,7 @@ hwaddr memory_region_section_get_iotlb(CPUArchState *env,
>              iotlb |= PHYS_SECTION_ROM;
>          }
>      } else {
> -        iotlb = section - address_space_memory.dispatch->sections;
> +        iotlb = section - address_space_memory.dispatch->map.sections;
>          iotlb += xlat;
>      }
>  
> @@ -747,23 +740,23 @@ void phys_mem_set_alloc(void *(*alloc)(size_t))
>      phys_mem_alloc = alloc;
>  }
>  
> -static uint16_t phys_section_add(MemoryRegionSection *section)
> +static uint16_t phys_section_add(PhysPageMap *map,
> +                                 MemoryRegionSection *section)
>  {
>      /* The physical section number is ORed with a page-aligned
>       * pointer to produce the iotlb entries.  Thus it should
>       * never overflow into the page-aligned value.
>       */
> -    assert(next_map.sections_nb < TARGET_PAGE_SIZE);
> +    assert(map->sections_nb < TARGET_PAGE_SIZE);
>  
> -    if (next_map.sections_nb == next_map.sections_nb_alloc) {
> -        next_map.sections_nb_alloc = MAX(next_map.sections_nb_alloc * 2,
> -                                         16);
> -        next_map.sections = g_renew(MemoryRegionSection, next_map.sections,
> -                                    next_map.sections_nb_alloc);
> +    if (map->sections_nb == map->sections_nb_alloc) {
> +        map->sections_nb_alloc = MAX(map->sections_nb_alloc * 2, 16);
> +        map->sections = g_renew(MemoryRegionSection, map->sections,
> +                                map->sections_nb_alloc);
>      }
> -    next_map.sections[next_map.sections_nb] = *section;
> +    map->sections[map->sections_nb] = *section;
>      memory_region_ref(section->mr);
> -    return next_map.sections_nb++;
> +    return map->sections_nb++;
>  }
>  
>  static void phys_section_destroy(MemoryRegion *mr)
> @@ -785,7 +778,6 @@ static void phys_sections_free(PhysPageMap *map)
>      }
>      g_free(map->sections);
>      g_free(map->nodes);
> -    g_free(map);
>  }
>  
>  static void register_subpage(AddressSpaceDispatch *d, MemoryRegionSection *section)
> @@ -794,7 +786,7 @@ static void register_subpage(AddressSpaceDispatch *d, MemoryRegionSection *secti
>      hwaddr base = section->offset_within_address_space
>          & TARGET_PAGE_MASK;
>      MemoryRegionSection *existing = phys_page_find(d->phys_map, base >> TARGET_PAGE_BITS,
> -                                                   next_map.nodes, next_map.sections);
> +                                                   d->map.nodes, d->map.sections);
>      MemoryRegionSection subsection = {
>          .offset_within_address_space = base,
>          .size = int128_make64(TARGET_PAGE_SIZE),
> @@ -807,13 +799,14 @@ static void register_subpage(AddressSpaceDispatch *d, MemoryRegionSection *secti
>          subpage = subpage_init(d->as, base);
>          subsection.mr = &subpage->iomem;
>          phys_page_set(d, base >> TARGET_PAGE_BITS, 1,
> -                      phys_section_add(&subsection));
> +                      phys_section_add(&d->map, &subsection));
>      } else {
>          subpage = container_of(existing->mr, subpage_t, iomem);
>      }
>      start = section->offset_within_address_space & ~TARGET_PAGE_MASK;
>      end = start + int128_get64(section->size) - 1;
> -    subpage_register(subpage, start, end, phys_section_add(section));
> +    subpage_register(subpage, start, end,
> +                     phys_section_add(&d->map, section));
>  }
>  
>  
> @@ -821,7 +814,7 @@ static void register_multipage(AddressSpaceDispatch *d,
>                                 MemoryRegionSection *section)
>  {
>      hwaddr start_addr = section->offset_within_address_space;
> -    uint16_t section_index = phys_section_add(section);
> +    uint16_t section_index = phys_section_add(&d->map, section);
>      uint64_t num_pages = int128_get64(int128_rshift(section->size,
>                                                      TARGET_PAGE_BITS));
>  
> @@ -1605,7 +1598,7 @@ static subpage_t *subpage_init(AddressSpace *as, hwaddr base)
>      return mmio;
>  }
>  
> -static uint16_t dummy_section(MemoryRegion *mr)
> +static uint16_t dummy_section(PhysPageMap *map, MemoryRegion *mr)
>  {
>      MemoryRegionSection section = {
>          .mr = mr,
> @@ -1614,12 +1607,13 @@ static uint16_t dummy_section(MemoryRegion *mr)
>          .size = int128_2_64(),
>      };
>  
> -    return phys_section_add(&section);
> +    return phys_section_add(map, &section);
>  }
>  
>  MemoryRegion *iotlb_to_region(hwaddr index)
>  {
> -    return address_space_memory.dispatch->sections[index & ~TARGET_PAGE_MASK].mr;
> +    return address_space_memory.dispatch->map.sections[
> +           index & ~TARGET_PAGE_MASK].mr;
>  }
>  
>  static void io_mem_init(void)
> @@ -1636,7 +1630,17 @@ static void io_mem_init(void)
>  static void mem_begin(MemoryListener *listener)
>  {
>      AddressSpace *as = container_of(listener, AddressSpace, dispatch_listener);
> -    AddressSpaceDispatch *d = g_new(AddressSpaceDispatch, 1);
> +    AddressSpaceDispatch *d = g_new0(AddressSpaceDispatch, 1);
> +    uint16_t n;
> +
> +    n = dummy_section(&d->map, &io_mem_unassigned);
> +    assert(n == PHYS_SECTION_UNASSIGNED);
> +    n = dummy_section(&d->map, &io_mem_notdirty);
> +    assert(n == PHYS_SECTION_NOTDIRTY);
> +    n = dummy_section(&d->map, &io_mem_rom);
> +    assert(n == PHYS_SECTION_ROM);
> +    n = dummy_section(&d->map, &io_mem_watch);
> +    assert(n == PHYS_SECTION_WATCH);
>  
>      d->phys_map  = (PhysPageEntry) { .ptr = PHYS_MAP_NODE_NIL, .is_leaf = 0 };
>      d->as = as;
> @@ -1649,37 +1653,12 @@ static void mem_commit(MemoryListener *listener)
>      AddressSpaceDispatch *cur = as->dispatch;
>      AddressSpaceDispatch *next = as->next_dispatch;
>  
> -    next->nodes = next_map.nodes;
> -    next->sections = next_map.sections;
> -
>      as->dispatch = next;
> -    g_free(cur);
> -}
> -
> -static void core_begin(MemoryListener *listener)
> -{
> -    uint16_t n;
>  
> -    prev_map = g_new(PhysPageMap, 1);
> -    *prev_map = next_map;
> -
> -    memset(&next_map, 0, sizeof(next_map));
> -    n = dummy_section(&io_mem_unassigned);
> -    assert(n == PHYS_SECTION_UNASSIGNED);
> -    n = dummy_section(&io_mem_notdirty);
> -    assert(n == PHYS_SECTION_NOTDIRTY);
> -    n = dummy_section(&io_mem_rom);
> -    assert(n == PHYS_SECTION_ROM);
> -    n = dummy_section(&io_mem_watch);
> -    assert(n == PHYS_SECTION_WATCH);
> -}
> -
> -/* This listener's commit run after the other AddressSpaceDispatch listeners'.
> - * All AddressSpaceDispatch instances have switched to the next map.
> - */
> -static void core_commit(MemoryListener *listener)
> -{
> -    phys_sections_free(prev_map);
> +    if (cur) {
> +        phys_sections_free(&cur->map);
> +        g_free(cur);
> +    }
>  }
>  
>  static void tcg_commit(MemoryListener *listener)
> @@ -1707,8 +1686,6 @@ static void core_log_global_stop(MemoryListener *listener)
>  }
>  
>  static MemoryListener core_memory_listener = {
> -    .begin = core_begin,
> -    .commit = core_commit,
>      .log_global_start = core_log_global_start,
>      .log_global_stop = core_log_global_stop,
>      .priority = 1,
> -- 
> 1.8.3.1