Il 13/05/2013 05:21, Liu Ping Fan ha scritto:
> From: Liu Ping Fan <pingf...@linux.vnet.ibm.com>
>
> Each address space listener has PhysPageMap *cur_map, *next_map,
> the switch from cur_map to next_map complete the RCU style. The
> mem_commit() do the switch, and it is against reader but AddressSpace's
> lock or later RCU mechanism (around address_space_translate() ).
>
> Signed-off-by: Liu Ping Fan <pingf...@linux.vnet.ibm.com>
> ---
> exec.c | 36 +++++++++++++++++++++++++++---------
> include/exec/memory-internal.h | 11 ++++++++++-
> 2 files changed, 37 insertions(+), 10 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index bb4e540..e5871d6 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -186,24 +186,26 @@ static void phys_page_set(AddressSpaceDispatch *d,
> hwaddr index, hwaddr nb,
> uint16_t leaf)
> {
> + PhysPageMap *map = d->next_map;
> /* Wildly overreserve - it doesn't matter much. */
> phys_map_node_reserve(3 * P_L2_LEVELS);
>
> - phys_page_set_level(&d->phys_map, &index, &nb, leaf, P_L2_LEVELS - 1);
> + phys_page_set_level(&map->root, &index, &nb, leaf, P_L2_LEVELS - 1);
> }
>
> static PhysSection *phys_section_find(AddressSpaceDispatch *d,
> hwaddr index)
> {
> - PhysPageEntry lp = d->phys_map;
> PhysPageEntry *p;
> - PhysSection *phys_sections = cur_pgtbl->phys_sections;
> - Node *phys_map_nodes = cur_pgtbl->phys_map_nodes;
> + PhysPageEntry lp = d->cur_map->root;
> + PhysPageTable *pgtbl = d->cur_map->pgtbl;
> + PhysSection *phys_sections = pgtbl->phys_sections;
> + Node *phys_map_nodes = pgtbl->phys_map_nodes;
> int i;
>
> for (i = P_L2_LEVELS - 1; i >= 0 && !lp.is_leaf; i--) {
> if (lp.ptr == PHYS_MAP_NODE_NIL) {
> - return &phys_sections[cur_pgtbl->phys_section_unassigned];
> + return &phys_sections[pgtbl->phys_section_unassigned];
> }
> p = phys_map_nodes[lp.ptr];
> lp = p[(index >> (i * L2_BITS)) & (L2_SIZE - 1)];
> @@ -234,7 +236,7 @@ MemoryRegionSection *address_space_translate(AddressSpace
> *as, hwaddr addr,
> IOMMUTLBEntry iotlb;
> MemoryRegionSection *section;
> hwaddr len = *plen;
> -
> + PhysPageTable *pgtbl = cur_pgtbl;
d->cur_map->pgtbl.
> for (;;) {
> section = address_space_lookup_region(as, addr);
>
> @@ -254,7 +256,7 @@ MemoryRegionSection *address_space_translate(AddressSpace
> *as, hwaddr addr,
> | (addr & iotlb.addr_mask));
> len = MIN(len, (addr | iotlb.addr_mask) - addr + 1);
> if (!iotlb.perm[is_write]) {
> - section =
> &cur_pgtbl->phys_sections[cur_pgtbl->phys_section_unassigned].section;
> + section =
> &pgtbl->phys_sections[pgtbl->phys_section_unassigned].section;
> break;
> }
>
> @@ -1703,7 +1705,21 @@ static void mem_begin(MemoryListener *listener)
> {
> AddressSpaceDispatch *d = container_of(listener, AddressSpaceDispatch,
> listener);
>
> - d->phys_map.ptr = PHYS_MAP_NODE_NIL;
> + d->next_map = g_new0(PhysPageMap, 1);
> + d->next_map->pgtbl = next_pgtbl;
> +}
> +
> +static void mem_commit(MemoryListener *listener)
> +{
> + AddressSpaceDispatch *d = container_of(listener, AddressSpaceDispatch,
> listener);
> + PhysPageMap *m = d->cur_map;
> +
> + d->cur_map = d->next_map;
> + /* Fixme, Currently, we rely on biglock or address-space lock against
> + * reader. So here, we can safely drop it.
> + * After RCU, should change to call_rcu()
> + */
> + g_free(m);
> }
>
> static void core_begin(MemoryListener *listener)
> @@ -1771,11 +1787,12 @@ void address_space_init_dispatch(AddressSpace *as)
> {
> AddressSpaceDispatch *d = g_new(AddressSpaceDispatch, 1);
>
> - d->phys_map = (PhysPageEntry) { .ptr = PHYS_MAP_NODE_NIL, .is_leaf = 0
> };
> + d->cur_map = g_new0(PhysPageMap, 1);
> d->listener = (MemoryListener) {
> .begin = mem_begin,
> .region_add = mem_add,
> .region_nop = mem_add,
> + .commit = mem_commit,
> .priority = 0,
> };
> as->dispatch = d;
> @@ -1787,6 +1804,7 @@ void address_space_destroy_dispatch(AddressSpace *as)
> AddressSpaceDispatch *d = as->dispatch;
>
> memory_listener_unregister(&d->listener);
> + g_free(d->cur_map);
> g_free(d);
> as->dispatch = NULL;
> }
> diff --git a/include/exec/memory-internal.h b/include/exec/memory-internal.h
> index 1b156fd..0dfe260 100644
> --- a/include/exec/memory-internal.h
> +++ b/include/exec/memory-internal.h
> @@ -30,13 +30,22 @@ struct PhysPageEntry {
> uint16_t ptr : 15;
> };
>
> +struct PhysPageTable;
> +typedef struct PhysPageMap PhysPageMap;
> +
> +struct PhysPageMap {
> + PhysPageEntry root;
> + struct PhysPageTable *pgtbl;
cur_pgtbl should be introduced in patch 1 already.
> +};
> +
> typedef struct AddressSpaceDispatch AddressSpaceDispatch;
>
> struct AddressSpaceDispatch {
> /* This is a multi-level map on the physical address space.
> * The bottom level has pointers to MemoryRegionSections.
> */
> - PhysPageEntry phys_map;
> + PhysPageMap *cur_map;
> + PhysPageMap *next_map;
Pointers are quite expensive here. With RCU we can fetch a consistent
root/table pair like this:
rcu_read_lock();
do {
pgtbl = d->cur_pgtbl;
smp_rmb();
root = d->cur_root;
/* RCU ensures that d->cur_pgtbl remains alive, thus it cannot
* be recycled while this loop is running. If
* d->cur_pgtbl == pgtbl, the root is the right one for this
* pgtable.
*/
smp_rmb();
} while (d->cur_pgtbl == pgtbl);
...
rcu_read_unlock();
Remember to have a matching smp_wmb() in mem_commit, and to write ->root
first:
old_pgtbl = d->cur_pgtbl;
smp_wmb();
d->cur_root = d->next_root;
/* Write the root before updating the page table. */
smp_wmb();
d->cur_pgtbl = d->next_pgtbl;
/* Write cur_pgtbl before possibly destroying the old one. */
smp_mb();
page_table_unref(old_pgtbl); /* uses call_rcu if --refcount == 0 */
If you are renaming fields, please do it as the first step.
Paolo
> MemoryListener listener;
> };
>
>
