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RemoteAllocator: dequeue as destructive iterator

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This avoids repeated double-tapping domestication of the same pointer in
!QueueHeadsAreTame builds, by keeping the current "front" pointer to the queue
in trusted locations (stack, register) rather than storing it back to possibly
client-accessible memory.
This commit is contained in:
Nathaniel Wesley Filardo
2021-10-13 12:52:01 +01:00
committed by Nathaniel Wesley Filardo
parent 2316a5c574
commit ed10717dde
3 changed files with 67 additions and 52 deletions
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57
src/mem/corealloc.h
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@@ -418,37 +418,36 @@ namespace snmalloc
[local_state](freelist::QueuePtr p) SNMALLOC_FAST_PATH_LAMBDA {
return capptr_domesticate<SharedStateHandle>(local_state, p);
};
for (size_t i = 0; i < REMOTE_BATCH; i++)
{
auto p = message_queue().peek();
auto& entry = SharedStateHandle::Pagemap::get_metaentry(
local_state, snmalloc::address_cast(p));
std::pair<freelist::HeadPtr, bool> r;
if constexpr (SharedStateHandle::Options.QueueHeadsAreTame)
{
/*
* The front of the queue has already been validated; just change the
* annotating type.
*/
auto domesticate_first = [](freelist::QueuePtr p)
SNMALLOC_FAST_PATH_LAMBDA {
return freelist::HeadPtr(p.unsafe_ptr());
};
r =
message_queue().dequeue(key_global, domesticate_first, domesticate);
}
else
{
r = message_queue().dequeue(key_global, domesticate, domesticate);
}
if (unlikely(!r.second))
break;
size_t i = 0;
auto cb = [this, local_state, &need_post, &i](freelist::HeadPtr msg)
SNMALLOC_FAST_PATH_LAMBDA {
#ifdef SNMALLOC_TRACING
std::cout << "Handling remote" << std::endl;
std::cout << "Handling remote" << std::endl;
#endif
handle_dealloc_remote(entry, r.first.as_void(), need_post);
auto& entry = SharedStateHandle::Pagemap::get_metaentry(
local_state, snmalloc::address_cast(msg));
handle_dealloc_remote(entry, msg.as_void(), need_post);
return (i++ < REMOTE_BATCH);
};
if constexpr (SharedStateHandle::Options.QueueHeadsAreTame)
{
/*
* The front of the queue has already been validated; just change the
* annotating type.
*/
auto domesticate_first = [](freelist::QueuePtr p)
SNMALLOC_FAST_PATH_LAMBDA {
return freelist::HeadPtr(p.unsafe_ptr());
};
message_queue().dequeue(key_global, domesticate_first, domesticate, cb);
}
else
{
message_queue().dequeue(key_global, domesticate, domesticate, cb);
}
if (need_post)